The ecosystem of the St. Lucie River and Indian River Lagoon, one of the largest estuaries on Florida’s east coast, was historically very different from its condition today. Whereas the Caloosahatchee–Charlotte Harbor ecosystem had a minor, seasonal connection to the Kissimmee–Lake Okeechobee–Everglades watershed, the SLR-IRL ecosystem was isolated from any such surface connection. Nevertheless, it followed a parallel history of major hydrologic connections and resulting deleterious ecological changes. Periodic excessive freshwater releases from Lake Okeechobee, together with other changes to the estuary, have reduced its former ecological integrity.
Prior to 1892, the Indian River Lagoon and the St. Lucie River had been predominantly a freshwater to lightly brackish environment, without a local outlet to the Atlantic Ocean. In 1892, residents determined to get navigable ocean access dug through Hutchinson Island, and the St. Lucie Inlet was born. The constrained freshwater ecology of the Indian River Lagoon and St. Lucie River transitioned to a tidal estuarine system, and new ecological values developed. The changed ecosystem attained the greatest species diversity of any estuary in North America.
Many alterations of the St. Lucie River and Indian River Lagoon estuary have damaged its ecology. In addition to drained watersheds, nutrient-laden agriculture and residential runoff, it is the redirected excess waters from Lake Okeechobee, coming through the St. Lucie canal that have most dramatically stressed the estuary, overwhelming the estuary with episodic freshwater releases causing sudden, drastic salinity reductions since the 1920s.