Curiosities: Why are some lake algae toxic?

A: The answer is unclear, said Katherine McMahon, an associate professor of civil engineering at UW-Madison, and an expert on cyanobacteria, as the blue-green algae are known to science. “This is the bazillion dollar question,” she said. “Certain cyanobacteria simply don?t have the genes to make toxins, while others have the genes, but don?t always make the toxins.”