Proportion of lakes and reservoirs surveyed in Region 8
Pollutants and processes impacting surveyed waters

The data presented here were assembled from 305(b) reports produced by the six states in EPA Region 8 (Colorado, Montana, North Dakota, South Dakota, Utah, Wyoming). It should be noted that comparisons of water quality between states can be inappropriate due to different survey methods and water quality criteria. This Regional summary of water quality in lakes and reservoirs can be used to determine pollutants and processes affecting water quality in the six-state area and the rigor of state monitoring programs in Region 8.

The data presented were assembled from 305(b) reports produced by the six states in EPA Region 8 (Colorado, Montana, North Dakota, South Dakota, Utah, Wyoming).

Detailed water quality information, measured on the scale of individual watersheds, is available at EPA's Surf Your Watershed website.

A total of 3,225,614 lake and reservoir acres exist in the six states that make up EPA Region 8. New methods of measurement, along with more complete state definitions of impounded waters, will result in a more accurate total and an increase in the total acreage for the Region. In general, the total acres of lakes and reservoirs is underestimated for the Region.

One of the goals for 305(b) reporting is for comprehensive coverage characterizing all waters in each state, tribe, and participating jurisdiction. Region 8 is close to meeting that goal for lakes and reservoirs. Water quality conditions were surveyed in 2,090,161 lake and reservoir acres , representing 64.5% of the Region's 3.3 million acres of lakes, reservoirs and ponds. All water-quality assessments apply exclusively to surveyed waters and cannot be extrapolated to describe the conditions of the region's lakes, reservoirs, and ponds as a whole.

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A number of pollutants were identified as impacting surveyed lakes in the 1998 State 305(b) reports. From these surveys, it was found that nutrients are the most widespread pollutant impacting surveyed lakes, impairing 40% of the surveyed lake and reservoir acres.

Healthy lake ecosystems contain nutrients in small quantities from natural sources, but extra inputs of nutrients (primarily nitrogen and phosphorus) unbalance lake ecosystems. When temperature and light conditions are favorable, excessive nutrients stimulate population explosions of undesirable algae and aquatic weeds. After they die, algae sink to the lake bottom where bacteria consume the available dissolved oxygen as they decompose the algae. Fish kills and foul odors may result if dissolved oxygen is depleted.

Other significant pollutants in Region 8 include metals, oxygen-depleting substances, siltation, and suspended solids. Impairment due to metals may reflect the detection of mercury in fish tissue samples. It is difficult to measure mercury in ambient water, and many states rely on fish samples to indicate mercury contamination, since mercury bioaccumulates in tissue. The extent of the mercury problem is complex, because it involves air pollution.

Agriculture is the leading source of pollutants impairing surveyed lakes and reservoirs in Region 8. Agriculture generates pollutants that degrade aquatic life or interfere with public use of 36% of the Region's surveyed lake and reservoir acres.

Other leading sources of pollution include point sources, hydromodification, flow regulation, and urban runoff/storm sewers. Point sources include permitted discharges from both industrial and municipal wastewater treatment plants. Region 8 States have noted an increase in atmospheric deposition as a source of pollution in lakes. This is due, in part, to a growing awareness of the magnitude of the atmospheric deposition problem. Researchers have found significant impacts to ecosystem and human health from atmospherically delivered pollutants.

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