High-Volume Freshwater Discharges

A problem particular to the southern IRL is freshwater discharge from Lake Okeechobee. Much of the lake’s water results from stormwater runoff from metropolitan Orlando and the Kissimmee River watershed and from rainfall in the area around the lake.

During the rainy season, increased water volume filling the lake puts pressure on the aging Herbert Hoover Dike. The dike surrounds the lake and could cause life-threatening flooding if it were to fail.

To prevent stress, the U.S. Army Corps of Engineers channels water from Lake Okeechobee to the IRL on Florida’s east coast and the Caloosahatchee River on Florida’s west coast.

Billions of gallons of freshwater can release and enter the Lagoon daily when lake levels are particularly high. When these discharges last long periods, the normally brackish (partially salty) water in the St. Lucie River Estuary, which drains to the Lagoon, becomes fresh. This dramatic salinity shift has detrimental effects:

• Devastates shellfish beds
• Harms seagrasses
• Potentially triggers massive blooms of toxic cyanobacteria, blue-green algae that thrive in freshwater

These blooms can persist for long times due to the excessive nutrient loads in the water from Lake Okeechobee and the surrounding basins. Sediments carried with these freshwater releases also cause problems. They sometimes turn the water nearly black as the plume moves from the lake to the St. Lucie River to the IRL and out to the ocean.