A photo from NASA shows the scope of the algae problem in Lake Okeechobee.
The space agency published two photos taken July 2 by the Operational Land Imager on the Landsat 8 satellite.
It said the bloom in the photos may contain blue-green algae but only a sample from the surface can confirm it.
NASA writes: Algae blooms are a regular phenomenon in Lake Okeechobee during the summertime. Pollution, such as runoff from farms, and lake water that warms through the summer, create an environment favorable for growth. This year the bloom grew large early in the season and it affected more people than usual, showing up far beyond the confines of the lakeshore.
The bloom covered 33 square miles in early May and the conditions that created it persist, according to NASA.