Ordinarily, businesses in South Florida would be preparing for a swarm of tourists this holiday weekend. This year, they're worried the only living thing on their beaches come the Fourth of July might be some putrid blue-green algae.

The algae, which the Washington Post compared to "thick, furry mold," "chunky guacamole," or a "festering, infected sore," has been coating waterways in four counties since late May, when algae in Lake Okeechobee tested positive for high levels of a toxin that targets the liver, according to the Environmental Protection Agency. Florida Governor Rick Scott declared a state of emergency over the blue-green sludge in Martin and St. Lucie Counties on Wednesday.

The blue-green algae is caused by bacteria that get energy through photosynthesis. These are called cyanobacteria, and they thrive in warm water. While the algae itself isn't toxic, it can release toxins as it dies. One of those is called microcystin, and though the EPA has limited data on its effects, acute cases of microcystin exposure can cause a range of nasty symptoms from headache, sore throat, vomiting and nausea, to cough, diarrhea, and pneumonia, according to a 2015 report. Residents in affected areas have complained of rashes and coughs, according to the Washington Post. Microcystin can persist for weeks or months in water, and the Florida Department of Environmental Protection has found it in some waters outside the lake.

Politicians of all stripes are calling the extent of the blooms unprecedented. Several beaches in the area have been closed to swimming, and locals are worried the unsightly blooms might put a damper on tourism over the holiday weekend.

Joe Catrambone of the Stuart Martin Chamber of Commerce told The Verge that the economic consequences for the small city of Stuart along the St. Lucie river could be devastating. "Boat rentals are at zero, which means marina sales for services, gasoline and food are zero," Catrambone says. "I can't put a pricetag on it, but certainly with a trickle-down effect it's in the millions of dollars for this weekend."

Ron Rose of the Jensen Beach Chamber of Commerce was more hopeful. "We've had a handful of people call and question about the situation because they've had reservations at local hotels. But everyone that has called has decided to come, because there's still sun in the sky and there's still unaffected beaches, and there's lots of things to see and do in Martin County," Rose tells The Verge.

Local Chambers of Commerce have been coordinating with the Business Development Board of Martin County to assess how many businesses are struggling due to the blooms. Almost 9 out of 10 of Martin County's businesses have fewer than 10 employees, says the Business Development Board's executive director Tim Dougher. If the slime turns people away this weekend and keeps them away, it might mean empty hotels, layoffs at restaurants and bars, and boats docked in harbors. Dougher said their current focus is reaching out to as many businesses as possible to understand the strain they're under and what kind of help they'd like. They hope to soon have access to other State and Federal programs, possibly including loans.

The blue-green algae originated in Lake Okeechobee, which is managed by the federal Army Corps of Engineers. The Corps has been struggling to protect the lake's fragile Herbert Hoover Dike and prevent it from bursting and flooding neighboring areas. To do so, the Corps tries to keep the lake's depth below 15.5 feet above sea level, said the Washington Post.

This has proved challenging because South Florida has been battered by above-average rains. This June, South Florida received 8.01 inches of rain, almost double what it saw in June 2015. The rains caused excessive runoff into Lake Okeechobee, and as water levels rose the Corps had to increase outflow from the lake to protect the dike. Between May 19 and 26, the volume of water discharged in the Caloosahatchee Estuary doubled and almost tripled in the St. Lucie Estuary. With this excess water came a lot of blue-green algae clogging rivers and canals, and washing out to sea.

Despite concerns over the multiplying blooms, the Army Corps of Engineers continued discharging high volumes of water through June, for fears that lake water levels would rise too high for the dam to contain. After Scott declared the state of emergency, the Corps relented and slowed flows. Starting today they will release 3,000 cubic feet per second into the Caloosahatchee Estuary, and 1,170 cubic feet per second into the St. Lucie Estuary, per a press release.

"That's a drop in the bucket, but at least it's something," says Catrambone.

While it might not be in time to help conditions this holiday weekend, he's hopeful summer tourism can still be saved. "We are pushing," he says. "We asked Senator Rubio today to get us a reprieve [from water discharge], get us two or three weeks, meet with the Corps, meet with the President, do whatever you can to give us a break."

Miami may be underwater by 2100