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.