Algae has covered about half of Lake Okeechobee—Florida’s largest freshwater lake—for much of June and early July 2023. The algae bloom led to the closure of parts of a marina and health warnings in neighboring counties.
Swirls and tendrils of blue-green algae can be seen in this image, acquired on June 12, 2023, by the Operational Land Imager-2 (OLI-2) on Landsat 9. Around this time, a NOAA analysis of Copernicus Sentinel-3 satellite data indicated that algae blooms covered about 380 square miles of the lake. That equates to more than half the area of the lake.
Blue-green algae, also known as cyanobacteria, are single-celled organisms that rely on photosynthesis to turn sunlight into food. The bacteria grow swiftly when nutrients like phosphorus and nitrogen are abundant in still water. The bloom pictured here may contain blue-green algae, as well as other types of phytoplankton; only a surface sample can confirm the exact composition of a bloom. Some cyanobacteria produce microcystin—a potent toxin that can irritate the skin and cause liver and kidney damage.
Microcystin was found in water samples taken from the lake on June 17 (five days after the image was acquired), including near the floodgate and canal used to release water into the St. Lucie Estuary on Florida’s southeastern coast. Excess lake water is typically released into the estuary and to farmlands to the south. But in mid-June, amid high lake levels, water managers prevented discharge because of the presence of harmful algae, according to the Miami Herald.
The Florida Department of Health in Lee, Martin, and Palm Beach counties issued public health warnings in late June and early July, cautioning residents not to swim or boat in the lake due to the presence of harmful algal toxins. The harmful bloom grew to cover 420 square miles on July 4, and spanned 440 square miles by July 11.
NASA Earth Observatory image by Wanmei Liang, using Landsat data from the U.S. Geological Survey. Story by Emily Cassidy.