Pristine aquatic ecosystems function in approximate steady state in which primary production of new plant biomass is sustained by N and P released as byproducts of microbial and animal metabolism. This balanced state is disrupted by human activities that artificially enrich water bodies with N and P, resulting in unnaturally high rates of plant production and accumulation of organic matter that can degrade water and habitat quality. These inputs may come from untreated sewage discharges, sewage treatment plants orrunoff of fertilizer from farm fields or suburban lawns. In some cases the climax stage of algal blooms can release toxic chemicals such as domoic acid to the aquatic environment, creating elevated metabolic risks to a variety of fish and marine mammals.