Cyanobacteria, also known as blue-green algae, can produce toxins and deplete lakes of oxygen when they die.  It can be dangerous for both pets and people. In August 2014, nearly half a million people in the Toledo area were without tap water for nearly three days due to contaminated drinking water. A type of blue-green algae, Microcystis, had produced particularly high levels of the liver toxin microcystin (MC) in Lake Erie.

Since the nutrient phosphorus is an important nutrient for these algae, and environmentalists and the politicians they influence don't understand biological systems thinking, they have made efforts to reduce phosphorus levels and inhibit the growth of cyanobacteria.

Scientists wish they would not make policy without considering all of the science. A new study using data beginning in 1958 shows simply reducing levels of phosphorus to control algal blooms in places like Lake Erie is actually helping the really toxic cyanobacteria strains, which can lead to an increase in toxins in the water.

Since there has been a shift in thinking about water management and adoption of an approach that reduces phosphorus and nitrogen loading in bodies of water, researchers used an agent-based model to simulate how cyanobacteria behave in Lake Erie. As the total number of cyanobacteria decreases, the remaining cyanobacteria have more of another important nutrient available: nitrogen. And higher concentrations of nitrogen help certain cyanobacteria to produce a toxin that protects them against damage resulting from oxidation.

Microcystin is a strong toxin for humans and animals but it’s highly beneficial for cyanobacteria. Microcystin can occupy certain sites on the enzymes important for life processes in the bacteria. In doing so, it shields the bacteria from aggressive hydrogen peroxide, which could otherwise attack these binding sites, oxidize the enzymes, and render them useless. Hydrogen peroxide is a by-product of photosynthesis so it's everywhere in nature. As such, producing microcystin is an important protective mechanism for the bacteria.

Some bacteria strains produce a lot of microcystin, and others which produce very little or none at all. A blanket approach disregarding this diversity among bacterial strains means a reduction in phosphorus can lead to an increase in Microcystin production. Phosphorus limited in nature so environmentalists have aggressively lobbied for cutting down on the use of phosphates as fertilizers in agriculture and reducing the phosphorus content of wastewater by means of tertiary treatment of wastewater to slow down the growth of blue-green algae, even in larger bodies of water such as Lake Erie.

Less blue-green algae means they also have to compete less for the other nutrients, the most important of which is nitrogen. And nitrogen, similar to phosphorus, is also only available in limited amounts. And, as it happens, it is an important element of the Microcystin  molecule. Those strains of bacteria which produce considerable amounts of microcystin can now do so more easily because microcystin also protects them from the harmful hydrogen peroxide.

The lesson: reducing phosphorus is a worthy goal, farmers don't want nutrients running off their land either, but activists treat agriculture as the enemy and advocate for policies to penalize food growers, but since reducing phosphorus will cause an increase in abundance of the subset of cyanobacteria that are able to produce toxin, resulting in more toxin overall, a balanced approach that includes more science and less political posturing is needed.