Five things to know about blue-green algae. (Yeah, it’s bad. And it’s getting worse.)

Three years ago, a foul-smelling blue-green algae bloom so thick it looked like guacamole shut down the beaches of Martin County over the Fourth of July. Last year, blue-green algae blooms again popped up in Lake Okeechobee and the rivers connected to it. This year, there are small blue-green algae blooms appearing in the waters of Pinellas, Manatee and Sarasota counties.

It could be worse. A blue-green algae bloom in the northern Gulf of Mexico spurred Mississippi authorities to close all 21 of their beaches over the weekend. In 2014, a blue-green algae bloom in Lake Erie meant 500,000 people were without a source of drinking water.

What is blue-green algae, why does it keep appearing and what does that mean for your health? Here are some answers.