The Clean Water Act of 1972 mandates that states must maintain a water quality standard to ensure fishable and swimmable surface waters. Waterbodies exceeding physical, biological, or chemical water quality standards must be reported semiannually to the USEPA per section 303(d) as threatened or impaired. States must then develop and implement a watershed plan for the listed waterbodies with the intent to reduce pollution, return to acceptable water quality parameters, and delist the waterbody. This research analyzed Oklahoma’s 303(d) lists from 2002-2022 and determined that 452 individual surface waterbodies were impaired for turbidity. Turbidity management is commonly accomplished with best management practices (BMPs) due to its nonpoint source nature. BMPs are costly, labor intensive to install, and often require coordination from multiple stakeholders; thus, it is imperative that BMPs are effectively installed and maintained for continued pollution reduction. Further analyses of Oklahoma’s 303(d) list identified 82 waterbodies that had been listed, delisted, and relisted for turbidity impairments within the study period. Three of these watersheds were modeled for the 20-year period using the Soil and Water Assessment Tool (SWAT). Watersheds were selected based on size, ecoregion, and documented management efforts. The baseline model excluded BMPs; whereas subsequent runs added BMPs that aligned with the Oklahoma Conservation Commission land management reports. This research aimed to assess BMP effectiveness, the impact of BMPs on sediment loading, and the adequacy of current design standards in a changing climate. The relationships between turbidity and other co-impairments were also analyzed to investigate pollutant pathways.
