Environment & Weather

Seaweed Plagues Palm Beach County Beaches With ‘Inundation’ Forecast

by
Daniel Nee
May 2, 2025

Beachgoers in Palm Beach County first began seeing piles of seaweed washing up along the shore about two weeks ago, leading to social media debates, conversations about whether it should be removed by local municipalities, and why it’s been hanging just offshore for so long. The reasons are numerous, from the end of a far-away drought, to fertilizer use halfway across the world, experts say. They have warned that the problem will likely get worse before it gets better – though the annoyance to swimmers may be beneficial to wildlife.

Seaweed, seen in black clumps, in the ocean in Boca Raton, FL, May 1, 2025. (Photo: Boca Daily News)

Sargassum washed up on the beach in Boca Raton, FL, May 2025. (Photo: Boca Daily News)

Colloquially known as seaweed, the vegetation rolling in the waves and accumulating on shore is sargassum, which develops in the Sargasso Sea, a region of the Atlantic Ocean bounded by four currents, centered off Florida with the aforementioned currents stretching from the west coast of Africa, to the east coast of South America, to the Canadian maritimes.

Sargassum is one of the few plant species of its kind to grow in warm water versus cold water, which makes its presence in Florida – and off the Florida coast – more common. The plant is unique in that it is free-floating, has air bladders that allow it to stay near the surface of the ocean, and provides a home for more than 100 other marine species that seek refuge in its body.

But why is so much washing up on local beaches this spring? The answer, according to researchers at the University of South Florida, can be found far to our south, and was predicted by the USF team more than a month ago.

“The increases in the Gulf of Mexico and western Caribbean Sea were typical as in most previous years, but total amounts in the eastern Caribbean Sea and west Atlantic reached surprisingly high levels,” a statement from the team said.

Sargassum washed up on the beach in Boca Raton, FL, May 2025. (Photo: Boca Daily News)

Seaweed, seen in black clumps, in the ocean in Boca Raton, FL, May 1, 2025. (Photo: Boca Daily News)

The amount of sargassum in the western Atlantic and Caribbean was 200 percent higher this month than their historical records in April. Similarly, the total amount in all regions combined was 150 percent higher than the historical record in April. Altogether, the total amount of sargassum observed in the region was 40 percent higher than the all-time high in June 2022, which makes 2025 a new record year.

“Most of these increases are due to both local growth and physical transport, but the exact reasons behind these new historical records need to be investigated,” the report said. “Corresponding to these increases, Sargassum beaching events have been reported around the Caribbean and along the southeast coast of Florida.”

Persistent southeast winds over the past month have brought the vegetation toward local beaches, as it floats between the coastline and the Gulf Stream offshore.

There are several theories – many of which can co-exist – as to why so much sargassum is growing in the warm waters of the Atlantic coast. Some of the blame comes from the increased usage of fertilizers in both the Amazon and Congo rivers, in South America and Africa, respectively. Experts have also cited more rain in the Amazon – after a long-time drought – that has propelled growth now that the river is actively flowing into the Atlantic Ocean again at a much higher pace.

The researchers are concerned because of the fact that the sargassum load has already reached an all-time record high in April, while historically, the largest amounts have been recorded in midsummer. This has led the USF team to begin forecasting sargassum blooms in advance – and the news isn’t great for local beachcombers.

Sargassum washed up on the beach in Boca Raton, FL, May 2025. (Photo: Boca Daily News)

Seaweed, seen in black clumps, in the ocean in Boca Raton, FL, May 1, 2025. (Photo: Boca Daily News)

“As in most previous years, May is expected to see continued increases in most regions,” the report said. “More Sargassum is expected to be transported to the west Caribbean Sea and then to the Gulf through the Yucatan. Sargassum inundation will continue to occur in most of the Caribbean nations and islands as well as along the southeast coast of Florida.”

In Florida, there is little officials can do to improve beach conditions, at least in the short term. Satellite imagery has identified about 31 million metric tons of sargassum contained in a “belt” between Africa and the Caribbean, and while the vegetation is not dangerous to swimmers, once the plant washes onshore, it can emit a foul odor as it decomposes and releases noxious gases as part of the process. The odor has been compared to that of rotten eggs.

As of March 1, governmental agencies in Florida are largely prohibited from performing beach raking with heavy equipment due to the presence of nesting sea turtles. Some municipalities have hired contractors to remove sargassum incrementally, but are only issued permits that allow its removal below the high water mark, where there are no nesting turtles. The sargassum, however, could have the ancillary benefit of providing a place of refuge for juvenile sea turtles as they hatch and make their way to the ocean – a silver lining for the benefit of nature, but still an inconvenience for beachgoers.