I just read at Mercola about Cyanobacteria.

Here is a summary of what I learned:

1. Cyanobacteria can be present in ponds with green water.
2. Cyanobacteria is called blue-green bacteria or blue-green algae.
3. It looks like spilled paint (or pea soup) and often floats to the shore.
4. Even a few mouthfuls can be lethal, particularly on dogs, cats, horses, cows and birds.

5. What is does is damage the liver and nervous system, respiratory tract infection, and skin, eyes, nose and throat irritation.

Hope this helps.