Rock Snot

A species of diatom that grows in warm and shallow water. If it overgrows, it can form large mats on the bottom of lakes, rivers and streams. It is not considered a significant human health risk, but it can affect stream habitats and sources of food for fish and make recreational activities unpleasant. It is considered a nuisance organism or invasive species. The microscopic alga can be spread in a single drop of water.