Nearly 240 square miles of Lake Okeechobee, the largest freshwater lake in Florida, are covered in a scum of blue-green algae that has also traveled down nearby waterways and out to the coastline.

The stinking sludge has impacted local ecosystems and the tourism industry and caused Gov. Rick Scott to declare a state of emergency in the affected counties.

The algae bloom is the result of a combination of factors, including the abundant nutrients washed in from surrounding agricultural lands, heavy winter rains, and hot, calm summer weather. In the future, such blooms could become more common as Earth’s rising temperature heats up lakes and oceans, providing a more favorable home for algae and other potentially toxic microorganisms in the water.