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.