What today's outlook actually tells you
The badge above is a Key Biscayne read of NOAA's daily Sargassum Inundation Risk map, plus a timestamped look at the Village beach cam. It is not a promise that Crandon North, Crandon South, or Cape Florida match that color.
Treat the colors as a planning hint, then verify on the sand:
- Low — little expected on shore. Still open the cam. A clean satellite pixel can miss a wrack line the rake has not reached.
- Warning — elevated. Go if you like, but have a backup plan.
- Medium — visible landings are likely. Walk the waterline before you unload the car.
- High — heavy mats expected. Skip the swim-through. Find a raked stretch or do something else.
We cache NOAA's latest published report for up to an hour. Maps newer than four days can set the current-risk badge. Older maps stay visible with an Outdated label and do not drive that badge. A fresh Village cam can raise concern. A clear view of one beach cannot declare the island low-risk.
When sargassum typically peaks
This is a seasonal pulse, not a daily guarantee. NOAA's Southeast and Caribbean disaster guide calls May through July the sargassum peak season. Florida FWC says abundance peaks in spring and summer, then ocean currents carry the rafts through the Caribbean and the Gulf to southeast Florida.
USF's Optical Oceanography Lab publishes the monthly Sargassum Outlook Bulletin. The September 30, 2026 bulletin says totals usually keep falling after summer, possibly into November, and that beaching on the southeast Florida coast continues, but not as severe as in the summer months.
Locally, the Village of Key Biscayne tells residents to expect large quantities in summer and early fall, and treats June through November — hurricane season — as seaweed season too. Northeast, east, and southeast winds usually dump more on the ocean beach.
A clean week in July does not end the season. A messy Monday in October does not mean every beach is shot. Use the monthly USF outlook for the basin. Use the daily SIR map and the cam for today.
Which Key Biscayne beaches usually catch it
The mats arrive from the Florida Straits onto the Atlantic side. That means the ocean-facing beaches:
- Village beach — the Village's own shoreline. Beach Raker rakes it seven days a week, usually from about 6 a.m. to 10 or 11 a.m. During turtle nesting, they wait for the morning nest survey and start later. This is the beach the cam shows.
- Crandon Park — the public Atlantic beach most visitors mean. North and South can differ by a few hundred yards. Do not assume the lot you parked in matches the waterline you saw on the cam.
- Bill Baggs / Cape Florida — another Atlantic stretch, and no lifeguards. If the ocean is piled, skip the swim and do the lighthouse or the bayside seawall.
The Village notes that more sand and seaweed pile up in front of Silver Sands, Key Colony, and Island House than along other parts of that oceanfront. Hobie is a bay shoreline on the causeway. It is not the Atlantic landing the Village is describing.
Skip this, do that
Short version, from someone who has walked these beaches on bad weeks:
- Skip swimming through the wrack. Walk until you find a raked gap. On the Village beach, that gap is more likely after the morning rake.
- Skip treating Miami Beach photos as a KB report. The island has its own wind and cleanup schedule. Open the Village cam.
- Skip assuming one beach speaks for all. Crandon can be groomed while Cape Florida still has a brown line. Check the stretch you will actually use.
- Do the cam, then the map, then the sand. If those three disagree, believe the waterline in front of you.
- Do something else if the ocean is a mess. Bill Baggs seawall, the lighthouse, or lunch. The beaches guide lists the fees and hours.
- Do check bacteria separately. Seaweed is not a Florida DOH advisory. See water quality today.
What sargassum is, and why it smells
Sargassum is free-floating brown seaweed. USF's Sargassum Watch System describes two pelagic species, Sargassum natans and Sargassum fluitans. FWC says the Great Atlantic Sargassum Belt has recurred each year since 2011, with large quantities coming inshore on Florida beaches in recent years.
As it decays it releases hydrogen sulfide, the rotten-egg smell. Florida DOH says that gas can irritate the eyes, nose, and throat, especially if you have asthma or another breathing condition. Leave if it bothers you. Do not tough it out for a sunset photo.
Skin irritation and stinging larvae
The weed itself does not sting. Tiny organisms living in it can. Florida DOH recommends avoiding contact with or swimming near sargassum. If you suspect stinging larvae, take the swimsuit off before you shower and wash it before wearing it again.
Is the water safe to swim?
Sargassum and bacterial advisories are separate calls. A beach can have seaweed and a Good bacteria sample. It can also look clear with an advisory in effect. Neither the seaweed map nor a Good sample proves swimming is safe.
For the official Florida Department of Health readings — Crandon North, Crandon South, Cape Florida, and the Village beach — use Key Biscayne water quality today. Glance at the beach flag for surf and marine life. Purple can fly with any other color when sea lice or jellyfish are in the water.
How we read the NOAA map
The map is NOAA's Sargassum Inundation Risk (SIR) product, built by AOML and USF from daily satellite imagery and surface-current models. We read the colors around the Key Biscayne coastline. That is a regional signal. It is not a lifeguard report.
On a heavy landing, the Village's contractor rakes the Village beach and, when the pile is too big to bury, hauls it. The Village says that can run to hundreds of truckloads in a season. That cleanup is for the Village shoreline. It does not clear Crandon or Cape Florida.