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Natrona County work highlights eliminating selenium to avoid wildlife, livestock problems

by Wyoming Livestock Roundup

According to the Wyoming Department of Environmental Quality (WDEQ), there are eight bodies of water in the state listed as impaired due to elevated presence of selenium. 

Lisa Ogden, Natrona County Conservation District manager, was a featured speaker at the inaugural Wyoming Association of Conservation Districts Watershed Conference, held in Casper Feb. 20-21, and presented on the dangers of selenosis in animals and how we can prevent it in our water systems.

Ogden was one of a variety of presenters who discussed projects to improve local watersheds at the conference. 

What is selenium 

Selenium comes from the Cody Shale that underlies much of Natrona County and is readily transported through our waterways,” said Ogden. “As per WDEQ impaired waters list, selenium in water bodies comes from both natural sources and irrigated crop production.” 

She explained selenium is a heavy metal, which makes it a high priority pollutant according to the Environmental Protection Agency (EPA). The metal is soluble in water, allowing it to easily travel throughout bodies of water. 

“It is the general consensus that irrigated crop production is the main cause of selenium in Wyoming waters,” said Ogden. “Precipitation and irrigation of selenium-rich soils can dissolve and mobilize the metal to the surface and ground waters.” 

“Selenium can bioaccumulate and form deposits in the topsoil,” she explained. “The metal is particularly concentrated in areas of pooled waters, such as ponding from flood irrigation or wetlands on selenium-rich soil.”


“Selenium is an essential trace mineral used to help the body make antioxidant enzymes, but too much of it can result in selenosis,” according to Ogden. “Selenosis has been documented in aquatic plants, invertebrates, reptiles and amphibians, as well as mammals including livestock, wildlife and humans.” 

She noted the standards for chronic and acute poisoning in animals are much lower than that of humans. 

“Animals have a much lower tolerance to selenium, especially aquatic animals,” she said. “EPA lists the chronic and acute standards for aquatic species at five and 20 micrograms respectively, while the human drinking water standard set by the EPA is 50 micrograms.”

She described the signs of livestock and wildlife selenosis as loss of hair, mane or tail, rough hair coat, sloughing of hooves, reduced reproductive performance, poor weight gain, hoof or horn changes, lameness and death. 

The signs for aquatic creatures include reduced egg hatchability, embryonic death and deformities, deformed or missing body parts, emaciation and death.

Minimizing selenium

“Research has shown flood irrigation has a stronger correlation to high levels of selenium than sprinklers,” according to Ogden. “Conversion from flood to sprinkler irrigation is not only more efficient but minimizes transport of selenium.” 

Ogden noted practices such as lining or piping ditches can also minimize selenium transport. 

“We also want to minimize development on wetlands and on soil rich in selenium,” said Ogden.  

She noted the success in delisting the North Platte River from the impaired water bodies list can be attributed to standard testing protocols. 

“Without good data, we have nothing,” Ogden said. “We don’t have the right to list, delist or claim something is good or bad without good data. Water quality data from 2012-17 had to pass rigorous testing from multiple organizations to delist the North Platte.” 

“As of 1995 only 10 percent of irrigated fields in the Kendrick Project Area were irrigated by sprinklers,” said Ogden. “The rest were irrigated by inefficient flood irrigation.” 

“We are happy to report since 2012, we have converted 1,200 acres from conventional flood irrigation to more efficient sprinklers, 70,000 feet of earthen conveyance ditch to pipelines and have made numerous stock wells, tanks and developments,” said Ogden.

Callie Hanson is the assistant editor of the Wyoming Livestock Roundup. Send comments on this article to

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