A harmful algae bloom 1.5 times the size of Rhode Island is heading toward Florida's Gulf Coast.

Elevated concentrations of Karenia brevis, the harmful organism that makes up "red tide," were reported 20 miles off the coast of Florida in the Gulf of Mexico, according to the Florida Fish and Wildlife Conservation Commission (FWC). According to satellite imagery estimates, the algae bloom is up to 60 miles wide and 90 miles long, Florida's biggest bloom since 2005.

"They are part of the natural system of the gulf, so we do get used to seeing them," Hayley Rutger, a spokesperson for the Mote Marine Laboratory and Aquarium, told the Orlando Sentinel. "This one is large, but not the largest we've ever seen."

The nearly annual harmful algae bloom (HAB) off the coast of Florida is often referred to as "red tide," because the bloom can turn the color of the ocean a brilliant red.

As NOAA notes, HABs are simply out of control algae blooms that produce microscopic toxins that can kill off animals and even cause humans to get sick. This year's edition has already killed off thousands of marine life, the FWC reports.

2013's HAB, which bloomed closer to shore, killed more than 200 of Florida's endangered manatees, NBC News reports.

The bloom is still some 20 miles off the Florida coast, but as ABC news reports, if the bloom gets within a mile of the shore it could start causing serious problems for residents there. Waves can break up the algae as the bloom moves closer to shore, sending the toxins airborne and making it difficult for residents along the shore to breathe.

In July, reports stated that toxic algae was expected to take over the shores of western Lake Eerie this year. A few weeks later, algae contaminated the drinking water in Toledo, Ohio.

The blooms form during the late summer and early fall, according to National Oceanic and Atmospheric Administration.

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