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What causes toxic algae?

Too much algae is slimy, stinky and unsightly — and it can also kill wildlife, pets and people.

What causes toxic algae?. Illustration by Patterson Clark

Algae blooms occur in warm waters polluted with excess nitrogen and phosphorus, nutrients that come from unregulated fertilizers and animal waste washed by rainfall into aquatic habitats. The algae are naturally occurring organisms, which overpopulate in an ecosystem out of balance.

Although they are called blue-green algae, the microbes are actually a cyanobacterium, which releases toxins that can damage liver and nerve cells. Some dogs attracted to the stench of the organism might ingest it, which can lead to a painful death. Swimmers can absorb the toxins through their skin.

Failed rural septic systems and poorly treated municipal sewage can add nutrients to the water to feed blue-green algae.

SOURCE: National Wildlife Federation.