Sargassum at Sombrero Beach, Marathon: today's conditions
First bulletin for this beach lands with tomorrow morning’s update.
Sombrero Beach faces the ocean on the south shore of Marathon, midway along the Florida Keys. This page tracks sargassum at Sombrero Beach day by day: what the seaweed line looked like this morning, a rating from 0 to 5, and a map that puts the beach alongside the other spots we follow in the Keys.
The report is refreshed every morning, before the first swim of the day, so you can plan the drive down the Overseas Highway with something better than a guess. You also get the trend of recent days, which matters as much as a single snapshot: rafts arrive in pulses with the wind, and a shoreline can look different from one day to the next.
Sombrero Beach on the sargassum map
What to know about this beach
Sombrero Beach opens due south, on the Atlantic side of Marathon. That is the windward face of the Keys: the easterly and south-easterly trades push whatever floats offshore straight toward the sand, and the rafts that ride north out of the Caribbean on the Florida Current travel along this same edge of the archipelago. Between the beach and the outer reef line, shallow water slows that drift without stopping it, so weed spotted offshore can take a day or two to reach the shore.
Season and wind direction change the picture. When a winter front swings the breeze into the north, it blows from the land on a south-facing beach and the waterline usually stays clearer. A settled south-east flow in spring or summer does the opposite and presses floating mats against the shore. The daily rating reflects that mix of fixed exposure and moving weather.
Frequently asked questions
Why does sargassum reach Sombrero Beach?
The beach faces due south on Marathon's ocean side. Easterly and south-easterly winds push drifting rafts, carried north from the Caribbean by the Florida Current, over the shallow channel and onto this stretch of sand.
How do I check Sombrero Beach before driving over?
Open the FanGass map the same morning. It is updated daily and gives Sombrero Beach a rating from 0 to 5, from clear sand to a heavy landing, along with the trend of the previous days.
When is sargassum most likely around Marathon?
Arrivals in the Keys cluster mainly from spring through late summer, when rafts drift up from the Caribbean. In winter, northerly winds behind cold fronts more often hold the floating weed offshore.
Does the offshore reef keep the seaweed away?
It calms the swell, not the sargassum. The weed floats at the surface, drifts over the reef line, then crosses the shallow channel before it reaches the sand, which can take a few hours to two days.