That red tide began in November 2017, killed thousands of fish, turtles and marine mammals and harmed the economy of coastal towns that rely on tourism. At its peak, it touched all three of Florida's coasts.

This red tide is currently only impacting the state's southwest coast. In addition to Collier County, Lee County also tested positive for low concentrations of the algae, The Associated Press reported.

It is not yet known how long this bloom will last or where it will spread, according to The Tampa Bay Times.

The University of South Florida's College of Marine Science predicted it would move northwest in the next few days, The Fort Myers News-Press reported.

Red tides are caused by the organism Karenia brevis. The Tampa Bay Times explained how these tiny organisms create such big problems:

Small, scattered colonies of microscopic Red Tide algae live in the Gulf of Mexico all year long. Usually their numbers are so tiny that no one notices. But every now and then, usually in the late summer or fall, the algae population 10 to 40 miles offshore explodes into something called a bloom.

During a bloom the algae multiply rapidly and spread across the water's surface, staining it a rusty color that gives the phenomenon its name. Then winds and currents carry it toward shore, where it can be fed and prolonged by pollution from fertilizer, sewage spills and leaky septic tanks.

So far, this red tide has killed hundreds of fish. The National Oceanic and Atmospheric Administration warned that those in the Naples area who have chronic respiratory illnesses or are especially sensitive to red tide will face breathing irritation, The Fort Myers News-Press reported.