JACKSON - Water in northern Wyoming is, in general, of higher quality than water in other areas of the country, according to a federal report studying the Yellowstone River Basin.

The U.S. Geological Survey conducted a three-year study of surface and ground water in the basin - from mountains to plains - and determined that most of the water's contaminants were naturally occurring.

"The arsenic level that exceeds drinking water standards is coming from geothermal sources in Yellowstone National Park," Kirk Miller, surface water hydrologist with the USGS said. "There's not much you can do about that."

Miller also said phosphorous is another big contaminant, coming from soils in northern Wyoming. Phosphorous can lead to algae blooms.

The Yellowstone River Basin was one of 51 areas studied by the USGS, under directive from Congress to assess the nation's water supply. The Yellowstone River Basin stretches from Yellowstone National Park on the west, down to Lander, east to Gillette and north to Montana's North Dakota border, where the Yellowstone River meets the Missouri River. The Montana area stretches from Livingston through Billings and Miles City to the state line.

The area was the largest of the 51 study areas, encompassing 70,000 square miles.

Human-introduced contaminants were not nearly as influential on water quality, Miller said.

"Pesticides, we have them but at very low concentrations," he said. "It's not like the mid-western streams."

Pesticide use was found mostly in water in the Bighorn basin, around Lander, Sheridan and Red Lodge, Mont.

Concentrations of fecal coliform bacteria and E. coli were higher in urban and agricultural streams than in forested or rangeland streams, the report said. Urban areas are where people live.

Cheryl Miller, another hydrologist with the USGS, said this bacteria comes from warm-blooded animals, most likely cattle.

"Almost 40 percent of the bacteria concentrations exceeded the federal recreational criterion for moderate use," she said.

There were high concentrations of phosphorous in the Clarks Fork, Yellowstone, Little Powder and Powder rivers, mostly due to natural sources.

"That was an important finding," Miller said. "There's obviously not a thing people can do to stop it."

Those phosphorous levels exceeded federal goals for reducing plant growth in flowing waters.

Concentrations of the trace element selenium were found in surface and ground water, but not in concentrations that will harm drinking water.

"Some of these high concentrations of trace elements are coming from these highly erodable soils like the Powder River Basin," Miller said. "Yes, people and grazing can help accelerate that, but the fact that these soils naturally contain it is where the source of it is."

Some selenium concentrations were found to be harmful to aquatic life, the report said.

Concentrations of radon in groundwater exceeded federal drinking water standards in some areas.

The team also looked at trends in surface water quality. Increased concentrations of sodium and chloride in the Powder River had occurred when oil-production water was discharged into Salt Creek from 1975 to 1988, but the situation has changed.

"Although discharge of oil-production water to Salt Creek has been reduced since 1988, the Powder River is currently of interest because of potential effects to water quality from discharge of water related to development of coalbed methane for energy supplies," the report said.

The study also said water quality and aquatic life in the Yellowstone River during the 1950s were "severely degraded by wastewater discharges from towns along the river," but conditions have improved because of wastewater treatment facilities.

The goal of the testing program is to come back and study water health at 10-year intervals.

"It's a national-scale effort and the idea is to synthesize this data on a national level," Kirk Miller said. "In general, water quality in the Yellowstone River Basin is good, when you put it in the context of the nation's water resources."