Miami-Dade County removes 9,000 tons of sargassum in July

Atlantic sargassum belt reaches second-highest level on record

Miami-Dade County crews removed 9,000 tons of sargassum from the county’s beaches in July, more than in any single month on record, as the brown algae continued to wash ashore across south Florida.

Chris Bumpus, chief of conservation for Miami-Dade’s parks, recreation and open spaces department, oversees cleanup of 17 miles (27km) of county beaches. Most mornings this time of year, a member of Bumpus’s seaweed crew walks on to South Beach around 7am to take pictures of piles of the stemmy, spicy-mustard-colored seaweed before a dozen tractors and specialized beach-combing vehicles are put to work trying to integrate the sargassum into the sand or rake it out to be hauled away.

“Back in July, the beach looked clean for about an hour,” Bumpus said. “Hopefully, by October it will die down. July is always the worst. It’s been a heavy season.”

Before cleanup begins, a crew marks new sea turtle nests so they are not harmed by the sargassum removal. The county holds a permit with the Florida Department of Environmental Protection for its use of heavy equipment to corral the seaweed, a permit that prohibits the equipment from 30 minutes before sunset until sunrise. About 700 sea turtles have built nests on county beaches this nesting season.

The county’s annual sargassum removal budget is funded by tourist development taxes paid by visitors who stay at hotels and short-term rentals. Miami-Dade spends $3m per year on the work, more than any other county in Florida, Bumpus said. The Florida Keys can see heavier accumulations because of the inlet-like shape of their beaches, he said. In July, Miami-Dade county commissioners voted to petition the state to allow the county more flexibility to use beach-raking equipment in more areas. The county started addressing the seaweed problem in 2019.

The record July total reflects a broader surge in the Atlantic. For centuries, sargassum grew in the Sargasso Sea, a region of the north Atlantic encircled by ocean currents that keep the seaweed concentrated there. In 2011, scientists saw the Great Atlantic Sargassum Belt form for the first time, stretching from west Africa to the Gulf of Mexico. Scientists say several factors contribute to the blooms, including nitrogen and phosphorus from rivers such as the Amazon, the Congo and the Mississippi, warmer water temperatures and ocean circulation.

Since 2011, the amount of sargassum has doubled every five years, and larger, denser mats have washed up in Mexico, Florida and the Caribbean. This summer, satellite imagery showed the second-highest amount of sargassum in the Great Atlantic Sargassum Belt at 33.5m tons, slightly behind 2025 when the seaweed biomass reached 38m tons.

Brian LaPointe, a research professor at Florida Atlantic University Harbor Branch who has studied sargassum since 1982, said the climate crisis is an indirect driver of the blooms. “As we see more ocean warming, we get more evaporation and that drives these extreme rain events that essentially flush more nutrients from land into the ocean,” he said. “So that’s an indirect effect that can increase nutrient supply to sargassum.”

“I think this year has been kind of a gamechanger in that we’ve seen major inundations here in south Florida, more than we’ve ever really seen in past years, and comparable to what’s been happening in the Caribbean, Mexico and the Dominican Republic,” LaPointe said.

Sargassum serves as critical habitat in the open ocean, but LaPointe said that changes as it approaches and comes ashore. “What we’re seeing is that as this excessive amount of sargassum comes ashore it’s affecting coral reefs and seagrass beds and creating dead zones, which strips the oxygen out of the water,” he said. “That’s why we’re getting these odors of hydrogen sulfide, which presents a human health risk.”

US federal and state agencies prohibit sargassum removal in open water over concerns for the sea life that lives in the floating mats. LaPointe said that could eventually change, as research in his lab is showing that sargassum loses much of its marine life as it deteriorates and approaches the beach. In Mexico, President Claudia Sheinbaum announced a $115m national plan to combat sargassum, including employing ships that scoop the seaweed out of the water.

LaPointe said more aggressive removal alone will not address the underlying causes of the blooms. “People are realizing this isn’t going away,” he said. “It’s getting worse. It’s the new normal. It’s not only treating the symptoms but doing more research on the land-based nutrient sources that we can do something about.”