What Nonpoint source pollution problems exist in Wyo

Nonpoint sources of pollution contribute to the majority of Wyoming’s surface water quality impairments. 

The three nonpoint source pollutants causing the majority of Wyoming’s surface water quality impairments are bacterial pathogens, sediment, and selenium.

Bacterial Pathogens

Nonpoint sources of pathogenic bacteria such as Escherichia coli commonly include faulty or inadequate septic systems, livestock operations, pet waste, and wildlife. Exposure to elevated levels of pathogenic bacteria can be a public health safety concern if contaminated water was accidentally ingested during recreation uses of the water body.


Eroding stream banks and surface runoff over bare land contribute sediment to Wyoming’s waters. Human land-disturbing activities that can contribute to erosion and sediment transport include:

  • Crop production
  • Construction
  • Roads
  • Overgrazing by livestock or wildlife
  • Timber harvesting
  • Urban development
  • Mining

Sediment loading increases turbidity which limits the amount of sunlight reaching aquatic plants and also affects fish spawning grounds and macroinvertebrate communities. In addition, sediment often transports other pollutants, such as phosphorus, nitrogen, pathogens, and heavy metals, which can attach to the sediment particles. 


Selenium is an essential trace element to humans and animals, but in higher concentrations can be toxic. Selenium bioaccumulates and can negatively impact fish and waterfowl reproduction. 

Selenium naturally occurs in the soils of several areas of Wyoming, particularly in areas derived from marine shales. Precipitation and irrigation of selenium rich soils can dissolve and mobilize selenium to surface and ground waters. 

Thus, while some sources of selenium occur naturally, anthropogenic activities that can increase selenium loading to surface waters include irrigated agriculture return flow, mining, and oil and gas production.