A major blue-green algae bloom spreads across western Lake Erie in this Landsat 8 image. Dense green areas reveal Microcystis cyanobacteria producing the toxin microcystin, reaching levels unsafe for recreation. Credit: Joshua Stevens, NASA Earth Observatory, using Landsat data from the U.S. Geological Survey During the warm months, Lake Erie becomes an ideal setting for cyanobacteria, also known as blue-green algae, to grow rapidly. Under these conditions, the algae can form large blooms that