Such blooms were common in the lake’s shallow western basin in the 1950s and 60s.
Phosphorus from farms, sewage, and industry fertilized the waters so that huge algae blooms developed year after year.
The blooms subsided a bit starting in the 1970s, when regulations and improvements in agriculture and sewage treatment limited the amount of phosphorus that reached the lake.
But in 2011, a giant bloom spread across the western basin once again. The reasons for the bloom are complex, but may be related to a rainy spring and invasive mussels.
The bloom in Lake Erie is mostly microcystis aeruginosa, a toxic algae that can harm the livers of mammals if ingested.
The image to the right of the central Great Lakes was taken by NASA’s Aqua satellite on October 9, 2011.
The icy blue swirls apparent in parts of Lake Michigan and Lake Huron are not composed of algae, but rather sediment that was churned up by a passing storm system in late September through the first of October.
Upwelling created by the winds brought quartz sand and silt from the bottom to the surface, says Richard Stumpf, an oceanographer with the National Oceanic and Atmospheric Administration.
The white sand looks milky blue when viewed through the water from space. It is a good tracer, says Stumpf, illustrating how circulation in the lake moves material from the banks to the center.
Full story and image: NASA