Reservoirs across Idaho nearing or at capacity
The Upper Snake River System is at 88% of capacity, according to the Bureau of Reclamation
Anderson Ranch Dam in Idaho’s Elmore County as seen on July 17, 2022. (Logan Finney/Idaho Reports).
The Upper Snake River Basin’s reservoir capacity is nearing its limit as the Portneuf River continues to flood, but the National Weather Service isn’t concerned about spillover from reservoirs in southeast Idaho.
Bureau of Reclamation data from Wednesday showed the Henry’s Lake and Grassy Lake reservoirs are at 100% capacity, while most of the reservoirs in the Upper Snake system are between 91 and 98% capacity.
Milner Reservoir is only 74% full, and Jackson Lake Reservoir is 71% full.
Collectively, the Upper Snake River System is at 88% of capacity, according to the Bureau of Reclamation.
There is a minor flood warning in place along the Portneuf River at Pocatello, affecting Bannock County. But Tim Axford, meteorologist at the National Weather Service in Pocatello, said there isn’t concern about the reservoirs overflowing.
“Not a lot of the snowpack is still around,” said Axford. “We melted out a lot of snow through May.”
There will also be additional demands for water due to irrigation that should use some of the water in those reservoirs, he said.
“There’s no indication they will be over topping,” Axford said about the reservoirs.
Most Idaho reservoirs are more full than last year, Bureau of Reclamation data show
Data on the Bureau of Reclamation’s website shows most of the reservoirs are more full than last year. For example, the American Falls Reservoir is holding about 111,125 more acre feet of water than what is its average. On Wednesday, the reservoir held a total of 1,552,594 acre feet of water.
Elsewhere in the state, Boise and Payette River Basins are also nearing capacity, as six of the seven reservoirs are at least 90% of capacity and systemwide the reservoirs are at 95% of capacity.
The National Weather Service has a flash flooding watch throughout the Treasure Valley due to rainfall. People in the area are warned to stay away from high water areas. Some areas of Wood River Valley have also experienced minor flooding over the last month.
Up in the Lewiston Orchards area, two smaller reservoirs are also at more than 90% of capacity.
The Bureau of Reclamation provides daily updates on the reservoir capacities as well as streamflow from surrounding rivers.
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