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Temperature can be a critical but often overlooked factor in the health of many aquatic environments. Certain fish, like trout, have extremely small tolerance ranges for temperature and dissolved oxygen levels, which are often linked. Increases in temperature of water can result from bacterial infestation and can lead to decreases in dissolved oxygen levels and/or algal blooms.

Though temperature of aquatic environments can fluctuate naturally seasonally, human interferences can interrupt these cycles. Thermal pollution often comes from coal and nuclear power plants, which use surrounding surface water to cool machinery and discharge this water back into the environment. As mentioned above, thermal pollution is closely linked with other pollutants. In some cases, colder water can also be released, such as from reservoirs, damaging environments that have naturally warmer waters.

An increase in the temperature of water can interrupt enzyme activity in many organisms or exceed the tolerance limits of some, leading to die-offs. Thermal pollution can also support algal blooms, which have deleterious effects in an aquatic environment.

Not much can be done about thermal pollution once it is present other than investigating the source of the problem. If the source is another pollutant, such as pathogens, alleviating this issue will likely take care of the temperature problem as well. Otherwise, some helpful steps are listed below.

Total Dissolved Solids

Total dissolved solids (TDS) indicate the amount of ions, including salts and metals, dissolved in a certain amount of water. Some dissolved ions in water are common, such as some CO 2 from respiration by organisms, or salts in saltwater. However, above certain levels, TDS can be detrimental to ecosystems. Anthropogenic sources of high TDS are common, and include agricultural/pesticide runoff, sewage discharge, or increased salinity from de-icing salts.

The implications of TDS can be extremely difficult to explore, as the measurement does not differentiate between the different ions dissolved in water. Some ions may be beneficial, like nutrients, while some may be deleterious, like metals. Each type of substance can have a different effect on the physiology of the organisms in the environment.

The best way to lower the TDS level of your local creeks or rivers is by prevention.


Toluene is a member of the benzene, toluene, ethylbenzene, and xylene (BTEX) group of pollutants, which are volatile organic compounds (VOCs). VOCs are certain compounds that participate in atmospheric photochemical reactions; in other words, VOCs aid in smog and ground-level ozone formation. Though VOCs are released by plants, they are released in much greater quantities by anthropogenic sources. Toluene is a component of paint thinners, adhesives, some inks, rubber, pesticides, and nail polish, is an additive to gasoline, and is used in leather tanning. It most commonly enters surface or groundwater through petroluem spills, which accounted for 90 percent of all toluene spills in 1993. Additionally, the EPA found that the pollutant was present in the water or soil at 63 percent of domestic hazardous waste sites in 1991.

Fish and other aquatic organisms are sensitive to both acute and chronic toluene exposure, which can cause major nervous system and neurological damage. Toluene is also most hazardous when absorbed through the skin, which is the most common point of entry for aquatic organisms.


Turbidity is the relative transparency of a fluid, in this case, surface water. The transparency depends on the amount of suspended particles in the water, so the measurement of turbidity is closely linked to total suspended solids. The particles suspended in the water can be almost anything, from silt to precipitated chemicals.

When surface water is turbid, less light enters the water, and aquatic plants cannot perform photosynthesis and less organisms can survive, thus lowering the productivity of the ecosystem. Turbidity is also linked with low dissolved oxygen, colder temperatures, harmed gill function, and degraded spawning areas. Fine particles can kill fish directly, as well.


In certain cases, it is not simple to identify the reason a stream is unhealthy or cannot support aquatic life without extended periods of monitoring. Most often, there are other types of pollution, such as siltation or loss of vegetation, found at these sites. There are, however, certain cases in which “unknown” is the only cause of impairment- at these sites, further monitoring and investigation is needed in order to facilitate the reestablishment of the biological community.

Specific Conductance

Specific conductance is a measure of how well water conducts electricity. High conductivity indicates substantial amounts of ions in the water, which can wreak havoc on aquatic ecosystems. Ions could range from chlorides, which come from road de-icers, to agricultural phosphates and nitrates, to iron, sulfate, copper, cadmium, arsenic, and others that often come from drainage from mines. Many of these ions can have negative human health effects as well, making it even more important to prevent their flow into our waterways. Cleanup and mitigation practices vary depending on the particular type of ions present.


As the use of water treatment plants and population increase worldwide, stress can be placed on water treatment plants, resulting in release of untreated sewage sludge. Additionally, the policy in much of the US is to treat storm-water in the same matter as sewage, meaning that in the event of prolonged rain, untreated sewage can be released into waterways. In more developing regions, water that has been “treated” may still contain dangerous pollutants.

Exposure of aquatic life to sewage sludge can result in a variety of issues. Foremost, sewage is filled with pathogens, which can lower the dissolved oxygen and raise the temperature of the ecosystem, rendering it unfavorable for many species. Pathogens in water cause an “oxygen sag,” in which there is a septic zone where no fish can survive. Additionally, sewage in water increases its turbidity, decreasing photosynthesis of aquatic plants and lowering the productivity of the ecosystem.


Pathogens’ presence indicates that water is contaminated by human or animal waste. Persons who come into contact with pathogens found in water can suffer headaches, diarrhea, cramps, nausea or other gastrointestinal illness. Two common pathogens found in water are Giardia and Cryptosporidium. These parasites are the cause of two of the most common waterborne diseases in the U.S. Both can persist in the environment for months and are highly resistant to disinfection. Young children and people with compromised immune systems may be particularly at risk from pathogens. Certain species of fish and wildlife are unaffected by these microbes while other species experience symptoms similar to humans.

Pathogens can enter waterways by way of sewer overflows, leaking sewer lines, and polluted stormwater that washes bacteria from undisposed pet waste into the nearest stream. Pet waste that is left in the street, dog park, or even a person’s backyard contributes to major water quality problems in Nashville. In agricultural areas, poorly chosen feeding, watering, and waste management locations can allow pathogens to make their way into our water. In rural settings, failing septic systems are often significant contributors to pathogen impairments.

In urban areas, high concentrations of pathogens are most often associated with heavy rainfall, which causes sewer system problems and carries pathogens from animal waste into our waterways.


Silt refers to the dirt, soil, or sediment that is carried and deposited by our water. While some silt in water is normal and healthy, many additional tons of silt find their way to our water every year, negatively impacting water quality. This pollution, known as siltation, results from erosion and land disturbing human activities, such as agriculture and construction.

Siltation negatively impacts ecosystems in many ways. Excessive silt clogs gills, and smothers eggs and nests. It can bury habitat aquatic insects need for survival, which impacts organisms up the food chain that eat these insects for survival. Siltation can also interfere with photosynthesis in aquatic plants resulting in a decrease in needed dissolved oxygen. Important components of aquatic habitat, which native aquatic species rely on for survival, are altered by siltation. These include the amount of light, the temperature, depth, and flow of water. In addition, pollutants like fertilizers, pathogens, pesticides, and heavy metals can be attached to soil particles that find their way to our water.

Siltation also increases levels of treatment needed for drinking water, fills up reservoirs and navigation channels, and increases a waterbodies likelihood of flooding.

Propylene Glycol

Propylene glycol is a small, carbon-based molecule that is in the alcohol family, along with the more familiar compounds ethanol (drinking alcohol) and isopropyl (rubbing alcohol). Propylene glycol is a common ingredient in pharmaceuticals, cosmetics and deodorant sticks. It also finds application as a de-icing compound and antifreeze.

Propylene Glycol is an organic contaminate in the same family chemicals like PCBs, DDT, chlordane, and dioxins, which are listed by the EPA as probable human carcinogens (cancer causing agents) and that tend to remain in the environment for an extremely long time. In some waterbodies, these substances have accumulated in sediment and pose a health threat to those that consume fish or shellfish.

Propylene glycol is known to exert high levels of biochemical oxygen demand (BOD) during degradation in surface waters. This process can adversely affect aquatic life by consuming oxygen needed by aquatic organisms for survival.

Problematically unhealthy levels of organic contaminates can be below current detection levels. Detection of these substances is generally made either by analyzing fish tissue levels and/or by use of sediment screening values provided by the EPA. Since organic contaminants can bioaccumulate in fish, it is important to make sure catfish and other species consumed by people are safe to eat. Children and pregnant or nursing women are the most sensitive sub- population.

Typically, propylene glycol finds its way to our water via production and processing facility wastewater, from spills, or from de-icing fluid carried by stormwater runoff.


pH is a measure of the relative amount of hydrogen and hydroxide ions in water. The values for pH range from 0 to 14 on a log scale, meaning that a difference of 1 is actually a monumental difference. Values from 0 to 7 are considered acidic, while those greater than 7 are alkaline. Naturally, the pH of surface water can vary from 6.5 to 8 without any repercussions to aquatic ecosystems.

The pH of surface or groundwater can change for a variety of reasons, both natural and anthropogenic. Organisms that release CO 2 when they respirate can contribute to acidification of the water, as CO 2 and water combine to form an acid. However, the more common reasons are acid runoff from abandoned mine sites or acid rain from nitrates and sulfates in the atmosphere. The type of bedrock present can greatly impact the pH of surface water in an area. For instance, if limestone is the most common rock in a region, such as in Tennessee, waters are more prone to be neutral or alkaline, as limestone is basic. Some other types of rocks can further decrease the pH of acidic liquids.

A low pH is a more common cause of issues than a high pH, although both occur. Acidic conditions can prevent fish from reproducing, or kill adult fish themselves. Additionally, metals are more toxic when conditions are acidic, and sediments are more prone to release toxic materials. In alkaline conditions, ammonia is more dangerous to organisms.

Oil and Grease

Oil and Grease includes a variety of substances including fuels, motor oil, lubricating oil, hydraulic oil, cooking oil, and animal-derived fats. The source of these substances are typically human derived. Oil and grease pollution can create chemical oxygen demand and reduce aquatic organisms’ ability to reproduce and survive. Though toxicity varies among different types of oils, refined oils are generally more toxic than crude oils.

Various hydrocarbons found in fuels can pose a wide range of human health problems, from affecting the liver, kidneys and blood to increasing the risk of cancer.


Odor is a useful indicator of water quality even though odor-free water is not necessarily safe to drink. Odor is also an indicator of the effectiveness of different kinds of treatment. However, present methods of measuring odor are still fairly subjective and the task of identifying an unacceptable level for each chemical in different waters requires more study. Also, some contaminant odors are noticeable even when present in extremely small amounts.

It can be expensive and very difficult to identify, much less remove, an odor-producing substance.


The main sources of nutrient impairments are over-fertilized agricultural lands, as well as urban lawns and gardens. Other sources include livestock, pet waste, municipal wastewater systems. Farmers apply nutrients in the form of chemical fertilizers, manure, and sludge. When fertilizers exceed plant needs, are left out in the open, or are applied just before it rains, nutrients can wash into our waterways over land or seep into groundwater.

Many backyard fertilizers for gardens or lawns contain nutrients. Just like in a rural setting, excess fertilizer that is not taken up by plants can seep into groundwater sources or be carried by stormwater over land to streams and rivers. Most dishwashing detergents are another source of nutrients that can be tracked back to the home. Finally, high concentrations of nutrients are also found in human and pet waste, which all too often contaminate our waters via leaking sewer lines or neglected pet waste.

These increased nutrient concentrations cause nuisance or toxic algae blooms in waterbodies. These blooms can ruin swimming and boating opportunities, create foul taste and odor in drinking water, and kill fish and aquatic life by removing oxygen from the water. High concentrations of nutrients must be filtered from our drinking water, since they can cause methemoglobinemia, a potentially fatal disease in infants, also known as blue baby syndrome.


Methylmercury is the form of mercury that is the most toxic to organisms. It originates as mercury, which is found naturally in many rocks and also originates from forest fires and volcanoes. The element is present naturally in trace amounts in the air, water, and soil. More notably, mercury is present in high amounts in coal, which, once burned, is deposited into waterways easily. This process causes the majority of anthropogenic mercury emissions worldwide.

Once present in waterways, mercury comes into contact with organic compounds, and is methylated to form methylmercury. Methylmercury is a liquid and can enter the ecosystem at the lowest trophic levels. From here, the methylmercury both bioaccumulates in each organism and biomagnifies to the top of the food chain. This means that the top predators in aquatic ecosystems are subjected to much higher mercury levels than are present ambiently in the water of the environment.

Methylmercury’s presence in these organisms can cause a variety of irreparable neurological, reproductive, and genetic issues. The ingestion of contaminated fish is the most common method of mercury exposure in humans, and this can cause many of the same issues. The most serious issues linked with methylmercury ingestion in humans are birth defects.


Manganese, like iron, is abundant in the Earth’s crust and many rock and soil types, and can be washed into waterways when these surfaces are eroded. The mineral also has many anthropogenic sources, such as petroleum processing or the additive MMT in fuel. According to the US EPA, manganese is currently detectable in 97 percent of US surface waters, but these levels are often well below safety limits. Though humans and animals require manganese to function, once it accumulates in an ecosystem, serious problems may result.

Precipitated manganese can render water turbid, decreasing the light entering the water and leading to fish and plant death. Excess ingested manganese in humans has been linked to muscular stiffness or weakness. In fish, it has been conclusively shown to cause a significant reduction in growth and reproduction as well as decreased white blood cell and hemoglobin counts in certain species. Unfortunately, not much information is available on the effects of manganese on aquatic ecosystems; due to their necessity at low doses, studies have neglected to investigate its more deleterious effects.

Because manganese is very difficult to remove from water, the focus tends to be on preventing its entry into the ecosystem. Manganese can be present in storm water runoff or effluent from industrial areas.


Lead is a non-essential heavy metal that is mined around the world and was once used for many commercial applications, such as paint. In fact, gasoline was an additive in fuel until 1976; once it was phased out, the average IQ of children in the US increased by 4 to 6 points. Lead is still continually added to our environment through the burning of fossil fuels. This pollutant is found in at least 75 percent of the US’s most polluted sites, according to the CDC.

In an ecosystem, lead can be extremely detrimental, as it is toxic to both plant and animal life. It has a tendency to bioaccumulate, meaning our cells have a tendency to gather it because it has similar properties to essential nutrients. Lead has also been shown to cause reduced fertility levels in mammals. Lead’s toxicity depends on its solubility, which depends on the water’s pH. When it enters the water, lead often reacts with sediments and organic matter.

Because the solubility and properties of lead largely depend on the water’s pH, lead removal tactics have variable success. There are, however, certain methods of removing lead form surface waters.


Iron is the fourth most abundant element in the earth’s crust, making up about 5% of its mass. Within humans and all other animals, iron plays a crucial role in carrying oxygen within the blood in the form of hemoglobin.

Though it is essential to aquatic organisms and humans, too much of the mineral in waterbodies is a significant hazard. At varying levels, it becomes toxic to different forms of aquatic life. In humans, Alzheimer’s and other neurodegenerative diseases, arteriosclerosis, diabetes mellitus, and other serious ailments have been linked to excess iron intake. Too much iron in our water can also cause algae blooms. Algal blooms result in lowered dissolved oxygen, which can cause fish kills and even produce neurotoxins.

Iron is typically transported into the environment through water and is naturally present in groundwater. However, water draining from abandoned mines, landfills, or other places where water comes into contact with rusting steel can elevate iron to toxic levels in our waterbodies.

Dissolved Oxygen

In fast-moving streams, rushing water is aerated by bubbles as it churns over rocks and falls down hundreds of tiny waterfalls, saturating these streams with oxygen. In slow, stagnant waters, oxygen only enters the top layer of water, and deeper water is often low in dissolved oxygen concentration due to decomposition of organic matter by bacteria that live on or near the bottom of the reservoir. Dams slow water down, and therefore can decrease the dissolved oxygen concentration of water downstream.

Additionally, bacteria decompose organic wastes, including leaves, grass clippings, dead plants or animals, animal droppings, and sewage, removing dissolved oxygen from the water when they breathe. Bacteria also use oxygen to digest dead algae, which bloom when fertilizers run off into waterways. If more food (organic waste or algae) is available for the bacteria, more bacteria will grow and use oxygen, and the dissolved oxygen concentration will drop.

Removing trees can also affect dissolved oxygen concentrations in different ways. In general, as water temperature increases, dissolved oxygen drops. The bare soil exposed from removing the tree can erode, increasing the amount of dissolved and suspended solids in the water and decreasing dissolved oxygen concentrations.

Depleted dissolved oxygen in water will restrict or eliminate aquatic life. While some species of fish and aquatic insects can tolerate lower levels of oxygen for short periods, prolonged exposure will affect biological diversity and in extreme cases, cause massive fish kills.


Naturally, chlorine is only found in combination with other elements, chiefly potassium. It also has a variety of anthropogenic uses, from wastewater treatment to road deicing, and runoff from industrial sources and roads can be contaminated with chlorine compounds. When chlorine compounds, especially from deicing, reach local waterways, there is a long-term storage effect of the chemicals, which leads to serious issues in the ecosystem.

There are many animals and plants in ecosystems that formed symbiotic relationships with bacteria long ago, which have now become essential to their survival. As a known antiseptic, chlorine can harm the microbiota of organisms that live in streams and lakes. These salts also increase the salinity of aquatic ecosystems, which throws the delicate balance of osmosis and diffusion in cells out of balance. Many organisms simply cannot function in these conditions.

Once chlorine is present in an ecosystem, it can take many years of clean conditions to flush the contamination out of the environment completely. Below are some ways to ensure chlorine will not enter your local waterways:

In-Stream Habitat Alteration

In-Stream Habitat Alteration refers to lost in-stream habitat due to human modification of a waterway’s bed, banks, or flow. Modification of a stream’s bed or banks happens when streams are channelized, sent through culverts, dammed, dredged or filled. Out of stream infrastructure, such as curbs and gutters, storm-drains, and concrete ditches alter the rate of flow that enters a stream, quickly ushering water off impervious surfaces and sending it rushing into the stream channel. These modifications to streams result in an alteration of in-stream habitat.

Habitat alteration can disrupt native species reproductive cycles or simply make living conditions untenable for some aquatics, reducing taxonomic richness and diversity. It can also lead to the replacement of native species by exotic or invasive species or provide advantages to generalist species over specialist species.

Hydrogen Sulfide

Hydrogen sulfide is a colorless gas with a rotten-egg odor. It is produced when bacteria break down plant and animal material, often in stagnant waters with low oxygen content such as bogs, swamps, or man-made lakes and reservoirs. Industrial sources of hydrogen sulfide include petroleum and natural gas extraction and refining, pulp and paper manufacturing, rayon textile production, chemical manufacturing and waste disposal. Some bacteria change calcium sulfate, the major component of wallboard, into hydrogen sulfide. If construction and demolition debris contain large quantities of wallboard, large amounts of hydrogen sulfide can be formed.

Besides bogs and swamps, other natural sources include volcanoes, hot springs, and underwater thermal vents.

Altered Streamside Vegetation

Altered streamside vegetation negatively impacts instream and streamside habitat and destabilizes stream banks. It involves the removal or modification of a waterway’s naturally vegetated banks. Common causes of this type of impairment include the removal of trees from stream banks and/or the mowing of stream banks. In agricultural areas, destabilization can result from animals grazing on and trampling streamside vegetation.

Healthy stream bank vegetation has many benefits. It provides:

  • A buffer zone that prevents pollutants from urban or agricultural stormwater from running off into a waterbody.
  • Roots that hold banks in place, preventing erosion and siltation.
  • Flood mitigation.
  • Habitat for fish and other aquatic life.
  • Canopy that shades the stream or river. This shading maintains naturally cool water temperatures critical to temperature sensitive species. Cooler temperatures also prevent excessive algal growth, which in turn prevents the occurrence of harmfully low dissolved oxygen levels.
  • A food source for aquatic invertebrates that eat fallen leaves and for fish that eat insects falling from trees.
  • Optimal streamside habitat consists of mature vegetation extending 35 to 100 feet from both banks of the stream.

Chloride is found naturally in seawater and certain minerals. However, the major source in which it enters the environment is through its use to deice roads during the winter, fertilizers, and sewage. Because they are extremely cheap and effective, Cl – compounds are used heavily during the winter to deice roads, ending up in surface waters everywhere.

Chloride is very soluble and mobile, compounding its effects as a pollutant. Additionally, once chloride has entered an ecosystem, it can take years to exit it, as there is no natural way it is metabolized or flushed from the organisms and water. It increases the salinity of these habitats, which can ruin the balance of osmosis and diffusion in cells, killing many organisms.


Aluminum is one of the most common elements in earth’s crust and is always present in the environment in conjunction with other elements, like silicon. Some of the aluminum present in the environment, however, results from anthropogenic sources, like air pollution, surface run-off, and waste from the mining and smelting processes. While aluminum can be tolerated in low concentrations, in high ones, it can be extremely deleterious in the environment. According to the EPA, one third of the most contaminated sites in the United States have aluminum pollution. In just Tennessee, 43 miles of streams are impaired abnormally high aluminum levels.

In humans, high aluminum intake has been linked to degenerative brain disorders like Alzheimer’s and Parkinson’s. As for the environmental impact, aluminum is accumulated in the tissues of some aquatic plants, which can be detrimental to health upon ingestion by other species, as aluminum acts as a neurotoxin in many mammals. The release of aluminum into the environment is often in conjunction with acid mine draining, which causes acidification of the environment.

Although there are some ways to remove aluminum from water, they tend to leave other chemicals behind. Thus, it is best to prevent more aluminum from entering.


Sulfates are compounds containing sulfur that cycle throughout the environment as part of natural biogeochemical cycles, which means they can enter aquatic ecosystems naturally. Methods of entry into freshwater ecosystems include saltwater intrusion, sea spray, and sea level rise. However, the majority of sulfates originate from surface runoff and air pollution, which is deposited into rivers through acid raid. Sulfates are often used in fertilizer, so pollution near these areas is the worst.

Sulfur compounds can have many detrimental effects on freshwater ecosystems. For instance, they promote the conversion of mercury into its most toxic form, methylmercury, and stimulate sediments to release nutrients, causing eutrophication. Some of the compounds themselves are also toxic to organisms within freshwater environments.