For water use purposes the greatest concern arises from the growth of blue-green algae in the water. Blue-green algae are in fact not algae at all, but are bacteria and their proper name is cyanobacteria.
Cyanobacteria produce both liver and brain toxins that can be as potent as cobra snake venom.
The cyanobacteria Microcystis , Anabaena , and Aphanizomenon are common on water reservoirs and lakes across the prairie region. The pictures below show a highly toxic strain of the cyanobacterium Microcystis. An agricultural stream in the foreground carrying clear, but nutrient-laden, water into a lake. This resulted in the proliferation of the cyanobacterium Microcystis . Close-up of the Microcystis bloom.