A lot of tourists head to Florida's sparkling, blue beaches for vacation. In fact, Florida is the top travel destination in the world with a record 105 million tourists visiting the state in 2015, according to Visit Florida, the official Florida tourism industry marketing corporation.

But this summer, many tourists are being greeted by thick layers of green rancid sludge on the water. These are blooms of blue-green algae, technically cyanobacteria, that have affected the water for miles along the Atlantic Coast near Palm Beach and parts of the Gulf Coast near Fort Myers Beach and Sanibel Island. The infestation is so bad that Gov. Rick Scott declared a state of emergency for Martin, St. Lucie, Lee and Palm Beach counties.

The governor asked the Department of Environmental Protection and the Florida Fish and Wildlife Conservation Commission "to take actions to address the issues caused by algal blooms in South Florida waterways," and asked the U.S. Army Corps of Engineers to reduce discharges from Lake Okeechobee.

Lake Okeechobee, it seems, is the problem. The nation's second largest freshwater lake and the largest lake in Florida, Lake Okeechobee is a repository for nutrient-rich runoff from surrounding farms and suburbs, reports the Tampa Bay Times. Those nutrients come from septic waste, fertilizer and manure. Because the dike built around the rim of the lake is aging and at risk of collapsing, the Army Corps of Engineers releases controlled discharges from the lake to protect nearby towns from flooding, according to the New York Times. When the polluted water hits areas downstream, the blend of fresh and saltwater, along with environmental factors such as warm weather, create ideal conditions for the blue-green algae to grow.

This started to happen in May when algae originally infested canals, rivers and estuaries, but because so many canals and rivers eventually empty into the ocean, beaches began to be affected.

Residents and tourists describe the sludge as "guacamole-like" with an odor like "dead, rotten fish."

"It smells like death on a cracker," nurse Cyndi Lenz told the Tampa Bay Times. Morgues don't smell as bad, she added.

Boats sit moored in green water while residents (and tourists) are stuck inside. Some people are wearing masks to avoid the stench.

But the algal bloom isn't just an annoyance. It can also cause health problems for people and animals, according to the Florida Fish and Wildlife Conservation Commission. Coming in direct contact with toxic algae through boating, swimming or water skiing may cause rashes, itchy eyes or sore throat. Ingesting contaminated water can cause diarrhea, nausea, vomiting and stomach pain. Animals can become extremely sick and may even die after ingesting the toxins in the algae.

green algae on an oar A resident shows off green algae she scooped on her oar while fishing in Estero Bay. (Photo: Rebekah Tiner Pierce/Facebook)

Hoping to bring an end to the problem, the Corps of Engineers has reduced the amount of water being released from Lake Okeechobee into local waterways and estuaries. The governor has called for federal aid to fund repairs to the dike, hoping for a long-term fix.

Since the end of May, eight manatee carcasses have been found in Florida's Indian River, reports the Orlando Sentinel. The animals had signs of the same trauma that has killed more than 150 manatees over the past four years. Researchers are still trying to pinpoint the exact cause, but say it is likely linked to an outbreak in algae — unrelated to the huge toxic outbreak in other parts of the state — that has decimated the sea grass that the manatees depend on for food.

Editor's note: This story has been updated with new information.

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.