| Summary: | Achieving total phosphorus (TP) total maximum daily loads (TMDL) for Lake Okeechobee (Florida, FL, USA), a large freshwater lake, is a key component of the greater Everglades ecosystem restoration and sustainability of south Florida. This study was aimed at identification of a cost-effective restoration alternative using four TP control strategies—Best Management Practices (BMPs), Dispersed Water Management (DWM), Wetland Restoration, and Stormwater Treatment Areas (STAs)—to achieve a flow-weighted mean TP concentration of 40 µg/L at lake inflow points, through a phased scenario analysis approach. The Watershed Assessment Model was used to simulate flow and phosphorus dynamics. The 10-year (1998⁻2007) ‘Base’ scenario calibration indicated ‘acceptable’ to ‘good’ performance with simulated annual average flows and TP load of 2.64 × 10<sup>9</sup> m<sup>3</sup> and 428.6 metric tons, respectively. Scenario results showed that TP load reduction without STAs would be around 11⁻40% with respect to Base compared to over 75% reduction requirement to achieve TMDL, indicating STAs as a necessary component to achieve restoration. The most cost-effective alternative to achieve TP target consisted of implementation of nutrient management BMPs, continuation of existing DWM projects, and the construction of ~200 km<sup>2</sup> of STAs for a total project cost of US $4.26 billion.
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