Paerl, H.W. et al. October 25, 2013. Blooms Bite the Hand That Feeds Them. Science Vol. 342 no. 6157 pp. 433-434 

Eutrophication from climate change, dams, higher carbon dioxide concentrations, drought, and nutrients from farm and urban runoff is increasing the size, duration, and toxicity of algal blooms in freshwater lakes and estuaries around the world, which threatens aquatic organisms, ecosystem health and human drinking water safety.

One of their toxins, microcystin, is a liver toxin and possible carcinogen.  Cyanobacteria go back around 3.5 billion years and are some of the oldest microorganisms on the planet, existing when there was no oxygen. They’re extremely adaptive, having survived ice ages, mass extinctions, and other disasters — so adaptive that now they’re threatening some of the life they once made possible.

Of the 123,000 lakes in America larger than 10 acres, at least a third may have these toxin producing cyanobacteria.

August 9, 2014. Don’t feed the Microbes. NewScientist.

THIS is not a health drink. The waters of North America’s Lake Erie turned lurid green this week, thanks to a bloom of toxic bacteria. The bloom has now receded and the water is drinkable again, but the challenge is to stop it happening again. The blue-green cyanobacteria Microcystis aeruginosa built up at the western end of the lake, which is the main source of drinking water for Toledo, Ohio. The bacterium produces a toxin called microcystin, forcing Toledo to turn off the water supply. Such blooms are increasingly common in Lake Erie, as phosphorus from fertilisers runs into the water and feeds the cyanobacteria. To prevent blooms, Ohio must stem the flow of phosphorus, says Jeffrey Reutter of Ohio State University in Columbus. Farmers should test soil to help them only use as much fertiliser as is necessary, and apply it when planting so unused phosphorus isn’t left lying around.