Many northern Wyoming residents were preparing to build an ark last week with what looked like the second coming of the great flood as rain and snowmelt combined to hit much of the state with more water than it has seen all year. The water soaked the ground and, along with melting mountain snow, filled Big Horn Lake at a rate of more than a foot a day for several days, prompting the Bureau of Reclamation to open the floodgates and increase outflows from the lake.


A National Weather Service station in Greybull recorded 1.85 inches of rain over the six-day period from May 21 through 27. A station in Cody recorded 3.28 inches. The most rainfall over the six days was recorded near Kaycee (7.64 inches) and Thermopolis (4.82 inches).


The U.S. Bureau of Reclamation increased releases to the Big Horn River from Yellowtail Dam Friday evening, May 23, from 1,500 cubic feet per second (cfs) to approximately 4,500 cfs over a three-day period.


According to a BuRec press release, the increases were necessary to help control the rate of fill of Big Horn Lake.
Inflows to Big Horn Lake were averaging about 8,000 cfs on Friday, May 23, based on National Weather Service stream flow forecast, and peaked around 14,000 cfs over the weekend. Since, inflows have slowed a little -- about 7,500 cfs as of Tuesday evening, May 27.


The U.S. Bureau of Reclamation May 1 spring snowmelt runoff forecast was expected to be above average (based on a 30-year average) for the Shoshone River Basin and below average for the Wind River Basin, but increased temperatures caused more mountain snow to melt and contributed to the water entering Big Horn Lake.


The move to increase outflows is in the opposite direction of a BuRec management decision earlier this month to reduce Big Horn Lake outflows from 1,950 cfs to 1,500 cfs in an attempt to increase the water level in the lake.


As of last week mid-week (May 21), Big Horn Lake recreationists were worried that boats could not be launched at Horseshoe Bend, but that fear has been swept away by rising water. As of Tuesday evening, the lake sat at 3,622 feet, about five and a half feet above the minimum launch level at Horseshoe Bend.


The Horseshoe Bend marina will now be open, said manager Lisa Dickerson, and boat tours will now be given on the weekends by Mark Garrison of Hidden Treasure Charters.


Further adjustments to releases during the next few weeks are likely depending on inflow conditions, according to the BuRec. Big Horn River recreationists are cautioned to be aware of changing flow conditions during this time.