Microcystis aeruginosa is a common species of cyanobacteria (often called blue-green algae) that blooms in the fresh and low salinity portions of the Chesapeake and Coastal Bays and can become quite striking if it floats and forms a surface scum. The water may show the appearance of blue-green paint floating or billowing near the surface. Ingestion of waters containing high concentrations of Microcystis can cause abdominal stress in humans leading to precautionary beach closures and can kill dogs and farm animals if they drink significant quantities of the bloom waters. There are many strains of Microcystis and during 2000 a toxic strain was identified from the Sassafras River. The Potomac River below Washington D.C. had massive blooms of Microcystis in the 1960’s and, although they still appear periodically in this region, these blooms have been reduced by improved wastewater treatment.
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