When the Army Corps of Engineers opens the S-80 structure southwest of Stuart, Florida, the St. Lucie River takes whatever the C-44 Canal has been carrying: lake water, runoff from thirty miles of drained basin, and in bad years cyanobacteria thick enough that residents photograph it next to their shoes for scale. It enters a tidal estuary where people fish for a living, where oyster reefs filter the water column, where the houses along the South Fork were bought on the assumption that the river would go on being a river.
The C-44 Canal runs from Lake Okeechobee east to S-80 and into the South Fork. On the lake's other side, the C-43 Canal carries water west through a series of locks to S-79, the Franklin Lock, the upstream boundary of the Caloosahatchee Estuary above Fort Myers. Both canals were dug to do what Wood's pumps did in New Orleans — take water off land so it could be farmed and built on. They also work as pressure-relief valves for Lake Okeechobee, moving water toward both coasts to protect the towns and farms ringing the lake.
The C-44 basin alone covers about 190 square miles. The system protects agricultural and developed land in Glades, Hendry, and Lee counties and takes load off the aging Herbert Hoover Dike, which holds back a shallow lake spread across 730 square miles. Whatever the water picks up on the way, it delivers.
What arrives
In Water Year 2025 the St. Lucie Estuary received roughly 1.09 million acre-feet of freshwater carrying 237 metric tons of phosphorus and 1,696 metric tons of nitrogen. The Caloosahatchee took 2.32 million acre-feet, with 441 metric tons of phosphorus and 3,647 metric tons of nitrogen. The nutrients don't come from one place. Over 2021 through 2025, the basins upstream of the Caloosahatchee supplied 63 percent of the phosphorus and 56 percent of the nitrogen reaching that estuary; the lake supplied 21 and 31 percent. Assigning blame to Okeechobee alone gets the accounting wrong, which matters when the fix is being designed.
Cyanobacteria are what make the discharge visible. In 2016 a bloom that started in the lake covered about 200 square miles and rode C-44 into the St. Lucie while the Corps drew the lake down to protect the dike. Martin County declared an emergency on June 29. In 2018, releases carried a large Microcystis bloom into both rivers. Sampling that August recorded biweekly mean microcystin concentrations of 205 parts per billion in the South Fork and 360 in the middle estuary — 25 to 45 times the EPA's recommended recreational threshold of 8 parts per billion.
Every element of that chain was doing its assigned job: the Corps protecting the dike, the dike protecting the towns around the lake, the canals draining the farmland.
Who lives at the receiving end
Stuart sits where the St. Lucie meets the Indian River Lagoon, a small city whose economy runs on the water: charter fishing, marinas, waterfront restaurants, and the visitors who come for a healthy estuary. Martin County's population is around 165,000. On the Gulf side, Fort Myers, Cape Coral, and the Lee County barrier islands run on the same economy. Clean water brings people and supports the fish that commercial and recreational operations depend on. The estuaries are the reason these towns are where they are.
When blooms arrive, health departments post toxin alerts telling people to stay out of the water, charters cancel, and waterfront values drop. In March 2024 the state issued alerts for the St. Lucie Canal at the 96th Street Bridge and for the St. Lucie River at Palm City Bridge, and Lee County followed with a Caloosahatchee alert a month later.
During the 2018 bloom, researchers took nasal swabs from 121 coastal residents. Microcystin turned up in 115 of them. People reporting recent contact with the water averaged 0.77 parts per billion; those without averaged 0.37. A follow-up recorded an average of 4.94 self-reported symptoms per participant, 74 percent respiratory, close to half ocular, 35 percent gastrointestinal. These were volunteers describing their own symptoms, not a controlled clinical study. They establish that people were carrying the toxin, not what it did to them over time.
The ecological accounting is firmer. A fifteen-year study of Caloosahatchee oysters found that sustained high-volume freshwater releases pushed salinity low enough to significantly reduce upstream oyster density, with extensive mortality associated with late-summer flows above roughly 2,000 cubic feet per second. A 2024 USGS reconstruction estimated about $5.5 million in lost recreational-boating value across four counties for July through September 2018, plus roughly $2.3 million in reduced single-family property values. The much larger tourism-loss figures often quoted for that year mostly reflect a simultaneous marine red tide on the Gulf coast — a different organism, Karenia brevis — and can't be charged to the canal discharge.
The fix that isn't finished
The Comprehensive Everglades Restoration Plan includes storage and treatment projects meant to hold water back before it reaches the estuaries. The C-44 reservoir and treatment area was physically completed in 2021 and is still in operational testing. In Water Year 2025 it stored an estimated 3,871 acre-feet and retained about 0.9 metric tons of phosphorus, against the 237 metric tons the estuary received that year. The water management district says the project can't be evaluated until every component is in routine operation, currently estimated for 2031. "Completed" and "operating" are five years apart here.
The C-43 reservoir, 170,000 acre-feet of capacity, opened in July 2025 and began initial filling; routine operation is anticipated in 2029. The EAA reservoir south of the lake, the one that would create real southward storage, is still under construction, also targeted for 2029.
A revised operating schedule for Lake Okeechobee took effect in August 2024, and modeling showed zero eastward lake releases across 95 percent of the simulated period. Models schedule releases; weather delivers water. In Water Year 2025, lake releases toward the Caloosahatchee dropped from the year before, but basin runoff rose enough that total flow through S-79 still came to about 1.87 million acre-feet. The agency reports make no claim that damaging high-volume discharge is behind them.
Until those reservoirs are running, what reaches Stuart and Fort Myers in a given year depends on how much rain falls on the lake and how much pressure the dike can safely be asked to hold. Neither of those keeps to a schedule.