Natrona County is home to nine (9) waterbodies that are listed on the Wyoming DEQ's 303(d) list for selenium impairment, including four ponds or reservoirs (Rasmus Lee Lake, Goose Lake, Illco Pond, and Thirty-three Mile Reservoir), five drainages or creeks (Poison Spring Creek, Oregon Trail Drain, Poison Spider Creek, and Casper Creek) and the North Platte River.
Section 303(d) of the Clean Water Act requires that states identify and list waters for which the effluent limits are not effective in attaining designated uses. The Clean Water Act requires that states develop a separate Total Maximum Daily Load (TMDL) for each pollutant/segment combination on the 303(d) list and prioritize waters based on the severity of each pollutant/segment combination or listing. TMDLs are to be completed on these impaired waters "to assure the protection and propagation of a balanced, indigenous population of shellfish, fish and wildlife, and allow recreational activities in and on the water". Each state must submit a 303(d) List of Impaired Waters to USEPA every two years. Wyoming Department of Environmental Quality's 2012 303(d) list is found here. A reduced version just highlighting the Middle North Platte Sub-Watershed is found here.
While selenium is a naturally occuring element and is an essential micronutrient for animals, in can be toxic in high concentrations. In plants, it occurs as a bystander mineral, sometimes in toxic proportions in forage.
