Yellowstone River Basin Water-Quality Assessment

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The Yellowstone River Basin (YELL) study-unit in Wyoming, Montana and North Dakota, is part of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program. The long-term goals of this program are to describe the status and trends in the quality of a large, representative part of the Nation's surface- and ground-water resources, and to provide a sound, scientific understanding of the primary factors affecting the quality of these resources. This web site will provide a focus for people who are interested in obtaining information about the program and obtaining access to data and publications relevant to water quality in the Yellowstone River Basin.

For details about the overall NAWQA Program, including program design and implementation, and early study unit findings since 1991, visit the NAWQA Program home page.


Major Water-Quality Issues

Major water-quality issues in the Yellowstone River Basin vary from potential degradation of pristine streams in headwater areas to industrial and agricultural effects in downstream reaches, and include both point and non-point sources. The issues generally are related to land and water use, but some are related to natural factors. Potential water-quality issues to be investigated include

  • Trace elements - Leachate from mine spoils and tailings can increase trace elements in both ground and surface water. Leaching of soils derived from marine shales of cretaceous age in some locations has caused elevated concentrations of selenium in water resources. Geothermal source areas, like those in the Yellowstone National Park area, can be sources for elevated concentrations of trace elements, such as arsenic, in both ground and surface water. Concentrations of radionuclides in water resources are a concern because of the widespread distribution of uranium-bearing rocks in the basin. Trace elements and phosphorus also can be associated with suspended sediments in surface water.

  • Toxic compounds - Potential sources of toxic compounds in both ground and surface water include: leachate from abandoned and active landfills; pesticides and fertilizers from lawns and croplands; hydrocarbons from leaking tanks, refining operations, pipelines, and spills; and waste from industrial and commercial activities.

  • Salinity - Increases in the salinity of both ground and surface water can occur from saline ground water disposal, irrigation return flows, and some irrigation practices.

  • Sedimentation - Loss of streambank vegetation, easily erodible soils, and many land-use activities can contribute to sediment problems in streams throughout the basin.

  • Bacteria - Fecal coliform bacteria concentrations can exceed water-quality guidelines for streams. New guidelines are being considered for Escherichia coli, a species of bacteria associated with waste from warm-blooded animals.

  • Nutrient concentrations - Nutrient concentrations in streams can exceed guidelines for the prevention of nuisance algal growths. Excessive concentrations of algae can result in inadequate dissolved-oxygen concentrations and harmful effects to aquatic life, as well as impeding aesthetic properties and recreational uses.

  • Low-density residential development - Low-density residential development in the outskirts of communities has the potential to affect ground-water quality in these areas. Potential influences include leachate from septic systems; fertilizer and pesticide use on lawns, pastures, and gardens; manure from horses and pets; and increases in road construction and vehicle traffic.

  • Other water-related issues - There are many other water-quality issues in the basin including: acidification of water resources by leaching of industrial wastes, increased concentrations of nutrients in surface and ground water, localized de-watering of sole-source aquifers, potential water-quality problems related to coalbed methane production and water-related concerns on tribal lands.


Surface-water, ground-water, and ecology data from the Yellowstone River Basin NAWQA study unit and other study units that overlap into Wyoming (Upper Snake River, Great Salt Lake Basins, and South Platte River) are available from the Water Quality Portal.

Additional data files are archived at