To Miami’s Chagrin, Warming Seas Are Driving a Bumper Crop of Sargassum
This story was originally published by the Guardian and is reproduced here as part of the Climate Desk collaboration. Dealing with seaweed is the bulk of Chris Bumpus’s job during the summer. As chief of conservation for Miami-Dade county’s parks, recreation and open spaces department, Bumpus is in charge of cleaning sargassum off 17 miles […]
As summer approaches, Chris Bumpus faces an ever-growing challenge in his role as chief of conservation for Miami-Dade county’s parks, recreation and open spaces department. His main duty involves clearing sargassum, a type of floating brown algae, from 17 miles of county beaches. The situation has worsened, with more and more sargassum washing up on the shores of South Florida, West Africa, the Gulf of Mexico, and the Caribbean.
During morning walks to South Beach, Bumpus’s crew photographs the piles of brown, mustard-colored seaweed before employing tractors and specialized vehicles to incorporate the sargassum into the sand or remove it for disposal. In July alone, they cleared 9,000 tons of sargassum, the highest amount removed in a single month. "July is always the worst," Bumpus explained, "It's been a heavy season."
Before commencing the cleanup, a team marks any new sea turtle nests to avoid any harm caused by the sargassum removal. So far this nesting season, approximately 700 sea turtles have laid eggs on county beaches. Miami-Dade county allocates $3 million annually towards sargassum removal, more than any other county in Florida.
The Florida Keys experience heavier sargassum accumulation due to their inlet-like beach shape. For centuries, sargassum thrived in the Sargasso Sea, an area in the north Atlantic surrounded by ocean currents that keep the seaweed concentrated there. However, in 2011, scientists observed the formation of the Great Atlantic Sargassum Belt for the first time, stretching from West Africa to the Gulf of Mexico.
Scientists attribute the increased occurrence of sargassum blooms to factors like nitrogen and phosphorus from rivers, warmer water temperatures, and ocean circulation. Since 2011, sargassum levels have doubled every five years, leading to larger and denser mats washing up in Mexico, Florida, and the Caribbean. Satellite imagery in July revealed the second-highest amount of sargassum in the Great Atlantic Sargassum Belt, with 33.5 million tons, just behind the 38 million tons recorded in 2025.
Climate change has also exacerbated the sargassum proliferation, according to Brian LaPointe, a research professor at Florida Atlantic University Harbor Branch. Increased ocean warming leads to greater evaporation, causing extreme rain events that flush more nutrients from land into the ocean, indirectly boosting the nutrient supply for sargassum growth. Miami-Dade county started addressing its seaweed problem in 2019, with the annual budget funded by tourist development taxes.
The county now seeks state approval to use beach raking equipment in more areas, aiming to tackle the seaweed issue more effectively. While the US prohibits sargassum removal in open water due to concerns for sea life, LaPointe believes this policy might change as research in his lab shows that sargassum loses its marine life as it deteriorates and approaches the beach.
The seaweed serves as a critical habitat in the open ocean, but its impact changes when it reaches the shores. It negatively affects coral reefs, seagrass beds, and creates dead zones, leading to low oxygen levels and hydrogen sulfide emissions, posing a potential human health risk.
Written by urgent.news from Mother Jones's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
