These TMDLs address certain DO and nutrient impairments in the Indian River Lagoon Basin. Specifically, DO and nutrient TMDL rules being proposed for adoption are for the Eau Gallie River, Crane Creek, the C-54 Canal at Confluence with the Sebastian River, the South Prong Sebastian River Estuary Segment, and the Sebastian River above the Indian River. DO-only TMDLs are being proposed for Addison Creek, the North Prong Sebastian River, and the South Prong Sebastian River Freshwater Segment. These waterbodies were verified for nutrient and/or DO impairments due to elevated chlorophyll a concentrations and/or depressed DO concentrations using the methodology established in Chapter 62-303, F.A.C., Identification of Impaired Surface Waters. Based on results from water quality modeling and statistical analyses, it was demonstrated that the low DO condition in these impaired waters were mainly caused by loads of biochemical oxygen demand (BOD) and sediment oxygen demand (SOD) resulting from the long-term accumulation of BOD in the sediment. Therefore, BOD loading limits were established by these proposed TMDLs to restore the DO condition in these impaired waters. Using statistical analyses of spatial and temporal patterns of nutrient-related data in nutrient impaired waters, it was determined that the observed elevation in chlorophyll a concentrations in most nutrient impaired water segments, except for the Eau Gallie River, were mainly caused by receiving water processes under extreme weather conditions instead of by elevated watershed nutrient loadings. Therefore, the nutrient loading targets for nutrient impaired water segments were established to be consistent with the nutrient loading targets adopted previously into this rule to protect the seagrass communities in the mainstem of Indian River Lagoon. Because the Eau Gallie River showed consistent long-term elevation in chlorophyll a concentration compared to other water segments in the same area, nutrient reduction goals more stringent than those adopted previously for the same watershed area were establish to restore the nutrient condition in the river. The watershed nutrient and BOD loads were simulated using the Hydrological Simulation Program – Fortran (HSPF) and the Pollutant Load Screening Model (PLSM). The DO and chlorophyll a dynamics in receiving waters were simulated using the HSPF model and the Environmental Fluid Dynamic Code (EFDC) model. This rulemaking has been given an OGC case number 12-1681.