A wet spring in the Midwest, combined with a heavy mountain snowpack and warming temperatures in Wyoming, is raising concerns about high water in the Big Horn Basin.

Flooding downstream prevented the U.S. Bureau of Recreation from releasing enough water through Yellowtail Dam to receive the expected inflow from the snowpack, and last weekend, the lake level rose into the flood-control allotment.

Monday afternoon, the elevation of the reservoir was slightly higher than 3,641 feet above sea level. Inflow into the reservoir Sunday was 19,864 cubic feet per second. The reservoir level has risen 9 feet since the first of June.

With higher temperatures expected this week and considerable snow left in the mountains, concerns have been raised that the lake level could threaten the causeway that takes U.S. 14-A over the south end of the reservoir east of Lovell. The driving surface on the causeway lies at 3,659 feet, one foot lower than the crest of the dam. If the water should rise to the top of the dam, the causeway bridge would have to be closed. Even if water rises only to the top of the flood control pool at 3,657 feet, it could threaten the structure of the bridge.

However, Steve Davies of the Bureau of Recreation Office in Billings, which manages Yellowtail Dam, said the current projection is that the lake will likely only reach 3,653 feet. Davies said the lake rose that high and flooded in 1997, and this year’s conditions are similar to that year.

Other roads around the south end of the lake, however, also may be threatened. Bob Croft of Friends of Big Horn Lake said there is concern for roads to John Blue Canyon and Cottonwood Canyon on the east side of lake as well as Crystal Creek Road that accesses ranches along Big Horn River south of U.S. 14-A.

Davies confirmed that, should the water reach 3,653 feet of elevation, roads in the Yellowtail Wildlife Habitat and on the east side of the reservoir, north of the highway, would be affected.

Cody Beers, public relations specialist for the Wyoming Highway Department in Riverton, said the department is watching the situation closely.

In 1967, U.S. 14-A was flooded and had to be closed, but the causeway was raised following that incident.

Upstream, outflows have been reduced at both Buffalo Bill and Boysen dams. Boysen was 66 percent full, 15 feet below its storage level and 22 feet below the top of its flood control level on Monday. Buffalo Bill was 65 percent full, almost 30 feet below its full level. Buffalo Bill, however, has no flood control allotment.

The only flooding reported in the Big Horn Basin was in south Big Horn County over the weekend. Paint Rock and Medicine Lodge creeks were out of their banks in the Hyattville area and the Medicine Lodge State Archaeological Site is closed.

The North and South Forks of the Shoshone River and the Clarks Fork of the Yellowstone River all came within a half a foot of reaching flood stage on Friday and Saturday, but caused very few problems and have since receded, said Park County Homeland Security Coordinator Mart Knapp.

“Right now, we’re holding our own,” he said.