Why did so many Florida manatees die in the Indian River Lagoon?

They starved. Manatees eat seagrass, and the Indian River Lagoon lost a very large share of its seagrass meadows over the 2010s after decades of nutrient pollution fed algae blooms that clouded the water and blocked the sunlight the grass needs. With their main food gone, manatees in the lagoon couldn't get enough to eat, especially in winter when they crowd into warm-water refuges. Florida recorded an Unusual Mortality Event, with a record number of manatee deaths — well over a thousand statewide in 2021, many of them in the lagoon. Boat strikes are a separate and serious killer, but the lagoon die-off was driven by starvation, not collisions.

Is feeding manatees lettuce a real solution?

No — it was an emergency stopgap, and the agencies running it said so plainly. During the worst winters, wildlife managers ran a supplemental feeding program at a warm-water site, handing out tons of lettuce to keep starving manatees alive through the cold months. It bought time and saved animals, but it doesn't fix anything. The only real fix is bringing the seagrass back, and the only way to do that is to cut the nutrient pollution clouding the water. Feeding wild manatees yourself is illegal and harmful — it teaches them to approach boats and docks. Leave the emergency feeding to the agencies.

What's one thing a homeowner near the lagoon can actually do?

Cut the nitrogen you send into the water. The biggest household levers are fertilizer and septic. Use less lawn fertilizer — or none — and never apply it before a heavy rain or during a local fertilizer-blackout period, because what your grass doesn't absorb washes into the lagoon and feeds the algae. If a sewer connection is offered for your old septic tank, take it; failing septic systems near the water are a major nitrogen source. Pick up pet waste, and support the muck-dredging, oyster, and seagrass-restoration projects your county is funding. No single yard saves the lagoon, but the pollution was built one yard at a time.

Blog statewide

The Indian River Lagoon Is Starving Its Manatees — And We Know Why

One of North America's most biodiverse estuaries lost most of its seagrass to decades of nutrient pollution. When the grass died, the manatees starved. Here's the chain — and how it gets unbroken.

by Silvio Alves May 3, 2026

A West Indian manatee swimming with her calf

A Florida manatee and her calf — Wikimedia Commons · Florida manatee mother and calf by Sam Farkas / NOAA · CC BY 2.0

A manatee is a strange thing to mourn. It’s enormous, slow, and faintly ridiculous — a thousand-pound animal that lives on grass and bumps gently into boats. For most of the last century, the Indian River Lagoon had thousands of them grazing its shallows. Then, over a few brutal winters, they began washing up dead by the hundreds.

They weren’t hit by boats. They weren’t sick with a virus. They were starving — in one of the most productive estuaries in North America, surrounded by water, with nothing left to eat.

The lagoon didn’t run out of manatees. It ran out of grass. The manatees followed.

This is the clearest, most heartbreaking example we have of how water pollution actually kills — slowly, indirectly, and entirely by our own hand. It is also, importantly, not hopeless. But to fix it you have to understand the chain.

What the lagoon is, and what it lost

The Indian River Lagoon runs about 150 miles down Florida’s central Atlantic coast, roughly from Ponce de Leon Inlet down to Jupiter Inlet — a long, shallow, brackish ribbon of water separated from the ocean by barrier islands. It’s one of the most biodiverse estuaries on the continent, home to thousands of species of plants and animals. Dolphins, sea turtles, wading birds, sportfish, and manatees all depend on it.

The foundation of all that life is seagrass — underwater meadows of grass rooted in the lagoon floor. Seagrass is nursery, shelter, oxygen, and food. It is, specifically, the main food of the West Indian manatee, which eats huge daily quantities of it to fuel that enormous body.

Over the 2010s, the lagoon lost a very large share of its seagrass — vast meadows simply gone. Not trimmed back. Gone. The bottom that once waved with green grass turned to bare mud and drifting algae.

The chain of cause

None of this was a mystery or an accident. It was a slow, cumulative chain, and every link is human.

Decades of nutrient pollution. Lawn and farm fertilizer, leaking septic systems, stormwater runoff, and a legacy of muck on the lagoon floor loaded the water with nitrogen and phosphorus — fertilizer, essentially, dumped into a closed estuary.
Algae blooms. Those nutrients fed enormous algae blooms. The water turned green and murky. Some blooms were so intense they crashed and triggered fish kills.
The light went out. Seagrass is a plant; it needs sunlight on the bottom. Murky, algae-choked water blocks that light. Starved of sun, the seagrass meadows died back massively.
The manatees starved. With their main food gone, manatees in the lagoon couldn’t eat enough — especially in winter, when they crowd into warm-water refuges and can’t simply leave to find grass elsewhere.

The result was an official Unusual Mortality Event. Florida recorded a record number of manatee deaths — well over a thousand statewide in 2021, many of them in the Indian River Lagoon, and many from starvation. Wildlife agencies took an extraordinary step they’d never taken before: a supplemental feeding program, handing out tons of lettuce at a warm-water site to keep manatees alive through the winter.

It worked, as a stopgap. It is not a fix. You cannot hand-feed your way out of an ecosystem collapse.

What’s being done — and what you can do

Here is the hopeful part, and it’s real. Cutting the nutrient load is hard and slow, but it’s underway, and where it’s worked the grass has started to come back. The toolbox:

Muck dredging — removing the decades-deep layer of nutrient-rich sediment from the lagoon floor.
Septic-to-sewer conversions — taking thousands of old septic tanks offline.
Stormwater upgrades and fertilizer ordinances — stopping nitrogen at the source.
Oyster and clam restoration — these filter feeders clean the water, and a healthy oyster bed clears a startling volume of it every day.
Seagrass replanting — replanting meadows where the water is clear enough to support them again.
Long-term nutrient-reduction targets — the official roadmaps for how much pollution has to come out, and by when.

Recovery is slow and depends entirely on cutting that nutrient load. But none of it is abstract, and a lot of it is downstream of ordinary choices. What an actual person near the lagoon can do:

Cut your yard fertilizer — use less or none, and never apply it before the rainy season or during a local fertilizer-blackout period. What your grass doesn’t take up runs straight into the lagoon.
Connect septic to sewer where it’s offered, and maintain the tank if it isn’t. Old, failing septic near the water is one of the worst nitrogen sources there is.
Pick up pet waste. It’s nitrogen too, and it washes in.
Support the restoration and the funding — oyster and seagrass projects, muck dredging, and the cleanup dollars on local ballots and budgets.
Give manatees space and obey no-wake and manatee zones. Boat strikes are a separate, major killer; slowing down in posted zones directly saves animals.
Report sick or dead manatees to the FWC Wildlife Alert hotline (1-888-404-3922). Quick reporting helps rescuers reach animals that can still be saved — and don’t feed wild manatees yourself; it’s illegal and harmful.

The honest part

This isn’t a far-off problem, and it isn’t one bad year. It’s a slow, human-caused unraveling that a legacy of muck makes genuinely hard to reverse — that sediment keeps releasing nutrients long after you stop adding new ones, so the lagoon doesn’t bounce back the moment we behave. The Indian River Lagoon is a bellwether for the rest of Florida’s coasts: what happened here can happen anywhere we overload an estuary with nitrogen.

But it is not hopeless, and saying so would be its own dishonesty. Where filter-feeder restoration, seagrass replanting, and real nutrient cuts have come together, patches of the lagoon have come back — clearer water, grass returning, the system slowly remembering how to be itself.

The manatees in the photo above are the whole argument. A mother and her calf, grazing in clear shallows, doing nothing but existing. They didn’t ask for any of this. The least we can do is give them their grass back.