Due to lower-than-normal precipitation in May and an early snowmelt in the Northwest, there will be less water available for salmon and steelhead this summer in the Columbia and Snake river basins as water supply forecasts are continuing their downward slide.
One of the largest declines in water supply is at Montana’s Hungry Horse Dam on the South Fork of the Flathead River where the Bureau of Reclamation’s water supply forecast fell by 28 percentage points from the May forecast of 87 percent of the 30 year average to 59 percent of average (535 thousand acre feet, June – July).
And, in central Washington the state’s Department of Ecology expanded its drought emergency declaration by 19 more watersheds, a result of lower than normal snowpack in addition to the early snowmelt on the east side of the state’s Cascade Mountains.
Ecology said in a news release that the warmer-than-normal April also led to rapid snowmelt – two to four weeks earlier than normal across the Central and North Cascades. This means that less water will be available in summer and early fall when it’s needed most for farms and fish.
“With an especially early spring snowmelt, we saw the need to take action to protect water supplies for the hot months ahead,” said Ecology Director Casey Sixkiller. “Expanding our drought declaration will make more of our state eligible for tools and funding to deal with drought impacts, and help us protect Washington’s farmers, fish and the communities that depend on snowmelt for their water supplies.”
There is no area in the Columbia River basin that has not been impacted by lower water supplies. Across the basin, June water supply forecasts dropped with few exceptions.
In British Columbia, water supplies at the two storage dams in the upper Columbia basin dropped. The water supply measured at Duncan Dam on the Duncan River dropped one percentage point in June to 85 percent of average (1,881 KAF, April – Sept) from the May forecast of 86 percent of normal. The Mica Dam water supply forecast dropped 4 percentage points from 86 percent to 82 percent of normal (10,699f KAF, Jan. – Sept.).
In one of the rare positive forecasts, the water supply at Libby Dam on the Kootenai River rose 2 percentage points to 77 percent of normal (4,670 KAF, April to Aug.) from the May forecast of 75 percent of normal. In May the water supply forecast at the dam set augmented flows for endangered Kootenai River white sturgeon at a Tier 2 level, the lowest level that provides flow augmentation for the sturgeon spawning.
See CBB, June 6, 2025, FLOW AUGMENTATION FROM MONTANA’S LIBBY DAM FOR ESA-LISTED KOOTENAI RIVER WHITE STURGEON BEGINS, HTTPS://COLUMBIABASINBULLETIN.ORG/FLOW-AUGMENTATION-FROM-MONTANAS-LIBBY-DAM-FOR-ESA-LISTED-KOOTENAI-RIVER-WHITE-STURGEON-BEGINS/
The Grand Coulee Dam June water supply forecast dropped 8 percentage points from 88 percent of normal (54,210 KAF) in May to 80 percent of normal (49,051 KAF, April – Sept). Grand Coulee in northern Washington is the culmination of water from the two British Columbia dams and Hungry Horse and Libby dams, both in the U.S.
Some of the largest drops in water supply were in the upper Snake River basin where the American Falls water supply forecast dropped to 52 percent of average, down 30 percentage points from the May forecast of 82 percent, continuing its precipitous drop in supply. American Falls had been over 100 percent of normal in April.
The forecasted water supply at the Lucky Peak Dam on the Boise River is higher than the May forecast. It’s 89 percent of normal (1,183 KAF, April – Sept) beats the May forecast of 85 percent of normal.
Still far below average is Dworshak Dam on the North Fork of the Clearwater River with a forecast now at 74 percent of normal (1,835 KAF, April – July), a drop from the May forecast of 80 percent of normal (2,095 KAF).
Water supply at Lower Granite Dam on the Snake River is 79 percent of normal (15,786 KAF, April – July), down 11 percentage points from the 90 percent of normal (20,116 KAF) in May.
And, the culmination of all the water that flows from the upper Columbia and Snake rivers is at The Dalles Dam where the June water supply is forecasted at 78 percent of normal (69,423 KAF, April – Aug), down from the May forecast of 85 percent of normal (75,683 KAF, April – August).
Water supplies over the summer are unlikely to improve, with NOAA’s June forecast at likely above normal temperature and below normal precipitation across the region. (See https://www.cpc.ncep.noaa.gov/products/predictions/30day/) The forecast through August is the same as the Northwest enters its typically driest time of the year (See https://www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal.php?lead=1).
The U.S. Drought Monitor is showing abnormally dry conditions in eastern Washington east of the Cascade Mountains, the Olympic Peninsula and areas of far eastern Washington, the Idaho panhandle and southern Idaho. In addition, in Oregon abnormally dry conditions prevail east of the Cascade Mountains and the far north east (https://www.drought.gov/watersheds/pacific-northwest).
In Washington, Ecology declared drought for the Yakima Basin watersheds on April 8, while issuing a drought advisory for Puget Sound region and portions of the Central and North Cascades, the state agency said in its news release.
Since then, conditions in all of Whatcom and Skagit counties, and portions of Snohomish, King, Pierce, Lewis, Thurston, Okanagan, Chelan, Clallam, Jefferson and Ferry counties have deteriorated due to early and rapid snowmelt, combined with unusually dry April and May weather, Ecology said.
Washington declares drought when there is less than 75 percent of normal water supply and there is the risk of undue hardship or impacts on water users and the environment, Ecology said. Both the hardship and water supply conditions were met in 19 watersheds – Nooksack, Lower Skagit-Samish, Upper Skagit, Stillaguamish, Snohomish, Cedar-Sammamish, Duwamish-Green, Puyallup-White, Nisqually, Chambers-Clover, Elwha-Dungeness, Methow, Okanogan, Chelan, Wenatchee, Entiat, Nespelem, Sanpoil, and Kettle.
“Drought this year is driven both by snowpack and precipitation deficits,” said Caroline Mellor, Ecology’s statewide drought lead. “While it’s normal for snow to melt in the spring, what we’ve seen over the last two months is unusually rapid, with snowpack melting away as much as 33 days earlier than normal in some river basins.”
Spring precipitation, Mellor said, was also low in parts of the state. April precipitation was 26 percent of normal in the eastern Cascade Mountains, 25 percent of normal in Central Puget Sound and 14 percent of normal in the Dungeness watershed.
Streamflow forecasts in multiple parts of the state are also low, Ecology said. The Chelan River is forecasted at 63 percent of normal, Methow River at 71 percent, Stehekin River at 68 percent and Okanogan at 48 percent, as of June 1. The last three rivers feed the Columbia River basin.
“These impacts illustrate the ways that snowpack drought impacts our water supplies in Washington,” Mellor said.
Studies predict that Washington can expect to see snowpack drought to occur 40 percent of the time by 2050.
“Even in the Evergreen State, our water supply is now less reliable in the summer and early fall than it was historically,” Mellor said. “We see the need to build resilience not for the possibility of water shortages, but the reality.”
For background, see:
— CBB, May 14, 2025, COLUMBIA BASIN SNOWMELT, RUNOFF IN MOST AREAS EARLY, RAPID; WATER SUPPLY FORECASTS MAY-SEPTEMBER DROPPING, HTTPS://COLUMBIABASINBULLETIN.ORG/COLUMBIA-BASIN-SNOWMELT-RUNOFF-IN-MOST-AREAS-EARLY-RAPID-WATER-SUPPLY-FORECASTS-MAY-SEPTEMBER-DROPPING/
— CBB, April 12, 2025, SOME MELTING IN MARCH BUT COLUMBIA BASIN WATER SUPPLY FORECAST IMPROVES, 90 PERCENT OF AVERAGE AT DALLES DAM (APRIL-SEPT), HTTPS://COLUMBIABASINBULLETIN.ORG/SOME-MELTING-IN-MARCH-BUT-COLUMBIA-BASIN-WATER-SUPPLY-FORECAST-IMPROVES-90-PERCENT-OF-AVERAGE-AT-DALLES-DAM-APRIL-SEPT/
— CBB, March 15, 2025, COLUMBIA BASIN WATER SUPPLY FORECAST, APRIL-SEPTEMBER, REMAINS BELOW NORMAL, COMING PRECIPITATION COULD HELP, HTTPS://COLUMBIABASINBULLETIN.ORG/COLUMBIA-BASIN-WATER-SUPPLY-FORECAST-APRIL-SEPTEMBER-REMAINS-BELOW-NORMAL-COMING-PRECIPITATION-COULD-HELP/
— CBB, February 7, 2025, THOUGH DOESN’T FEEL LIKE IT RIGHT NOW, COLUMBIA BASIN WATER SUPPLY FORECAST FOR APRIL-SEPTEMBER STILL DROPPING, HTTPS://COLUMBIABASINBULLETIN.ORG/THOUGH-DOESNT-FEEL-LIKE-IT-RIGHT-NOW-COLUMBIA-BASIN-WATER-SUPPLY-FORECAST-FOR-APRIL-SEPTEMBER-STILL-DROPPING/
— CBB, January 20, 2025, COLUMBIA RIVER BASIN SNOWPACK A MIXED BAG SO FAR, WATER SUPPLY FORECAST AT DALLES DAM (APRIL-AUGUST) NOW 89 PERCENT OF NORMAL, HTTPS://COLUMBIABASINBULLETIN.ORG/COLUMBIA-RIVER-BASIN-SNOWPACK-A-MIXED-BAG-SO-FAR-WATER-SUPPLY-FORECAST-AT-DALLES-DAM-APRIL-AUGUST-NOW-89-PERCENT-OF-NORMAL/