US Fish & Wildlife Service


Date of this Version



Published in Contaminant Report Number: R6/ 714C /99, 1-20, (1999)


Selenium is bioaccumulating in fish and aquatic birds inhabiting the Kendrick Reclamation Project (Kendrick) in Natrona County, Wyoming as a result of mobilization associated with irrigation return flows. Field studies conducted in the 1980’s by the U.S. Geological Survey (Survey) and the U.S. Fish and Wildlife Service (Service) as part of the Department of Interior’s National Irrigation Water Quality Program (NIWQP) revealed elevated selenium concentrations in water, sediment and biota at Kendrick and immediately downstream in the North Platte River. Selenium concentrations found in biota exceeded levels known to cause mortality and embryonic deformities in birds and impaired reproduction in fish. Additionally, reduced hatchability was documented in nesting aquatic birds.

Monitoring of selenium concentrations in water, sediment and biota was conducted by the Service and the Survey from 1992 to 1996 to assist the U.S. Bureau of Reclamation (Reclamation) in developing a remediation plan as well as to determine trends and assist in measuring remediation effectiveness. Selenium concentrations continue to exceed levels known to cause adverse effects to fish and aquatic birds. American avocet eggs collected from 1992 to 1996 contained selenium exceeding the 15 ug/g level known to cause impaired egg hatchability. In 1993, eight out of 62 (13 percent) addled avocet eggs contained deformities. Selenium concentrations in all pondweed and aquatic invertebrates exceeded the 3 ug/g dietary threshold for aquatic birds at all sites except 33-Mile Reservoir. At 33-Mile Reservoir all aquatic invertebrates exceeded the 3 ug/g dietary threshold for aquatic birds and pondweed exceeded this level in only two years of the five-year study. Wholebody selenium concentrations in rainbow trout collected from the North Platte River immediately downstream of Kendrick consistently exceeded the 4 ug/g level associated with reproductive impairment. Remediation planning for the selenium problem at Kendrick is ongoing.