Applied Ecology has recently completed a project which assisted FDEP in the refinement of total maximum daily loads (TMDLs) and load allocation within the Indian River Lagoon (IRL). The FDEP has identified the IRL and Banana River Lagoon (BRL) as impaired waterbodies due to nutrient over-enrichment. Since 2009, FDEP has issued TMDLs for the IRL and BRL requiring reductions of total nitrogen (TN) and total phosphorus (TP) in stormwater runoff and adopted Basin Management Action Plans (BMAPs) to meet the TMDLs for specific Project Zones of the BRL and the North IRL. Applied Ecology developed the Spatial Watershed Iterative Loading (SWIL) model as part of a study to update and refine the 2000 Pollutant Load Simulation Model (PLSM) used to assign the TMDLs for the IRL. SWIL is a custom ESRI ArcGIS toolset, originally designed to provide a continuous monthly simulation of runoff (surface and baseflows) over a 16-year period, yielding a more robust representation of pollutant loadings and freshwater volumes in the IRL. In comparison to the PLSM, SWIL incorporates more available data, more recent conditions, and more temporally fine datasets. Throughout the years, Applied Ecology has assisted FDEP in updating the load allocations of the IRL BMAPs through the use of the various SWIL model versions. The objective for this round of refinements was to estimate loads for current conditions across the IRL BMAPs (NIRL, CIRL, and BRL) based on a modified, updated SWIL 4.0 model version for the second 5-year BMAP cycle. The results from the analyses performed by Applied Ecology will be used by the FDEP to develop allocations using the adopted TMDLs.