Beaches along the Mississippi Gulf Coast remain closed because of toxic bacteria detected before Barry blew ashore.

Polluted Midwest floodwaters have fed an outbreak of cyanobacterium. Commonly known as blue-green algae, it can cause rashes, diarrhea and vomiting. It has spread eastward as water from the Mississippi River pours into the Gulf of Mexico.

Mississippi Department of Environmental Quality spokesman Robbie Wilbur says Monday the agency is continuing to test water samples. He says those tested Sunday “indicated the continued presence of algal bloom.”

The agency started closing some beaches June 22 along Mississippi’s mainland Gulf Coast. On July 7, it closed the last two sections near the Alabama line. Although the water is off limits, people can still be on the sand.

Mississippi’s barrier islands’ beaches have remained open.