Cool water is stacking up behind central Idaho's Dworshak Dam for use later this summer to chill warming water downstream in the Snake River for migrating salmon and steelhead.

It should be "less of a struggle this year" to decide how and when to deliver the North Fork of the Clearwater River's cold water, the Columbia River Inter-Tribal Fish Commission's Kyle Dittmer said during Wednesday's meeting of the Technical Management Team. The TMT's federal, state and tribal members discuss potential changes to federal Columbia/Snake river dam operations that can improve conditions for migrating salmon.

With a slow transition from winter to spring, water temperatures have generally been cooler than normal and the annual runoff of mountain snowpack got a late start.

"We have a cooler pool at Dworshak than we've had in previous years," said Jim Adams of the U.S. Army Corps of Engineers, which operates the dam. Those water temperatures this week ranged from about 39 degrees at the bottom of the reservoir to 64-65 degrees at the surface. The potential outlets, aside from spill gates, are well below the surface.

"We may have too much cool water," Adams said of the current situation's one potential problem. The U.S. Fish and Wildlife Service draws water from the river to rear juvenile steelhead, whose growth could be slowed if the water is too cold. Likewise fish in the North Fork and the Clearwater River need water warm enough allow steady growth.

Otherwise, current conditions offer "a good balance" for temperature control – keeping water temperatures downstream below 20 degrees C (about 68 degrees F) in July and September, Dittmer said. Returning adults don't fare as well during their migration, or on the spawning grounds, if temperatures rise above 68.

"We have a good opportunity no matter what we do," he said.

As of midweek the reservoir was 15 feet from full, having risen more than 110 feet since early May. The Corps has for the past week been releasing abut 15,000 cubic feet per second from the dam, the maximum of nearly 10 kcfs through the turbines and about 5 kcfs through spill gates. After peaking at 40 kcfs during the year's only hot spell in mid-May, flows into the reservoir have been mostly in the 22-24 kcfs range in June.

"There's a 100 percent chance that we're going to refill; it's just when. And we don't want to overfill," the Corps' Stephen Hall said. Filling too early could force additional spill that could stir up total dissolved gas above legal limits that pose harm to fish and other aquatic species.

"It's a pretty touchy year," Hall said of the balancing act. The goal is to fill by July 1, ahead of an always busy weekend at the reservoir for recreationists.

The Corps expects the inflows to remain strong. Hall said that most of the higher elevation SNO-TEL stations operated by the National Resources Conservation Service are showing a blanket of snow holding 40 inches of water.

"There's a lot of water up there," Hall said.

Adams said the Corps intended to reduce outflows to 12 kcfs by this weekend to slow refill and hopefully avoid the need to spill.

The Nez Perce Tribe's Dave Statler urged a scaling back to full powerhouse capacity, about 10 kcfs.

"You should not pass any more than is necessary, knowing we're going to have a declining hydrograph," Statler said of inflows that should soon begin to fall off. That would reduce the risk of having to spill.

Hall said the latest Northwest River Forecast update predicts that higher flows should continue in the near term.

A goal is to provide flow augmentation from the dam in summer, drawing it down from full pool (1,600 feet elevation) to 1,535 by the end of August, and 1,520 by the end of September. The water flows down the North Fork into the Clearwater and then the lower Snake River.

Given current river conditions and state of the cool-water reserve, Adams said water temperatures as measured at the lower Snake's Lower Granite Dam "should not exceed 65 degrees." Water temperatures are now at about 55-56 degrees.

"Last year we were pushing 68" during the third week in June, Adams said. The hydro and salmon managers have in the past on occasion had to tap Dworshak before July 4. Water at Clearwater and Snake monitoring stations above Lower Granite can rise into the 70s by the end of July.