The Story of the South Lagoon

Why does the water quality look so good when the sea grass is completely gone?

The South Lagoon is somewhat of a special case, where the watershed has been dramatically altered when the C-44 canal was constructed. The C-44 canal connects Lake Okeechobee to the south fork of the St. Lucie River that discharges into the South IRL Central. Lake Okeechobee is managed as a reservoir for large-scale agriculture. When there is a drought and the lake is low, water managers reserve water in the lake to use for agricultural irrigation. When it starts to rain and lake levels are high, billions of gallons of nutrient rich, silt laden, fresh water are discharged into the estuary causing toxic algae blooms, high turbidity, and low salinity. These conditions kill sea grass and are a threat to lagoon and human health.

The South IRL has three relatively large, well-spaced inlets that allow the lagoon water to exchange with the ocean. Water quality in the South IRL appears to be better than other regions like the Banana River or the Mosquito Lagoon. One reason is that the nutrients are quickly diluted by ocean water near the inlets. Secondly, even though salinity can be low after fresh water discharges from Lake Okeechobee, salinity is not being considered a health indicator because there are no established regulatory targets throughout the lagoon. Third, many monitoring stations have been discontinued and certain important water quality parameters (harmful algal blooms, for example), aren’t monitored at all.

Clearly, regulatory standards that examine nitrogen and phosphorus levels do not capture the picture of toxic algae, sudden salinity change, and turbidity that is effectively killing the South Lagoon. Nutrient pollution is a problem, but the elephant in the room for the South IRL is the Lake Okeechobee discharges.