Longer, cooler nights and a lowering of Round Butte-Pelton water release temperatures have served to make the mouth of central Oregon's Deschutes River an inviting place for spawning steelhead to pause and rest before continuing their spawning journey there or further up the Columbia-Snake river system.

"We're pulling in a lot of fish now," the Oregon Department of Fish and Wildlife's Rod French said. That's likely because the differential between the Columbia River water temperatures and those of the Deschutes has grown over the past few weeks. The lower Columbia was hovering around 70 degrees F at week's end. French said a check of the Deschutes near its mouth during the midday heat early this week showed a 65-degree reading.

"This is really the peak time of the year for fishing on the Deschutes," French said. Daily counts of steelhead downstream on the Columbia at Bonneville and The Dalles remain strong and fall chinook numbers are growing toward what is usually an early September peak.

Anglers in July complained that higher than normal water temperatures in the lower Deschutes were resulting in fewer steelhead stopping off and those that did were said to be less likely to bite. They blamed to some degree a newly instituted outflow regime from Round Butte-Pelton hydro project that resulted in warmer than normal early summer releases.

The hydro project includes Round Butte Dam, which is about 7 miles upstream from Pelton Dam. About 2.4 miles downstream from Pelton is a regulating dam. Round Butte backs up Lake Billy Chinook, which is filled by three major tributaries – Crooked, Metolius and upper Deschutes rivers.

The first of the dams was completed in 1958 and the last, Round Butte, in 1964. They have since effectively blocked up and downstream passage for salmon and steelhead stocks that were native to the three rivers.

A plan to provide passage at the dams and restore upstream salmon and steelhead stocks was developed as a part of the relicensing agreement for the projects. The dams are co-owned by Portland General Electric and the Confederated Tribes of Warm Springs (Wasco, Warm Springs and Paiute tribes).

A part of that plan was the construction of a "Selective Water Withdrawal Tower" at Round Butte, the uppermost dam, that draws water both from near the surface and from the bottom of Lake Billy Chinook. The tower, which went into full operation this year:

-- changes the reservoir currents to attract juvenile salmon and steelhead into the fish collection facility so they can be captured and transported around the dams and released back into the river to continue their journey toward the Pacific Ocean;

-- lowers the temperature of Lake Billy Chinook, providing healthier conditions for the fish,

-- modifies the temperature of the lower Deschutes River to more closely match what it was before the dams were constructed.

Those pre-dam conditions in the lower Deschutes were the result of a blending of cool Metolius waters and the warmer waters of the Crooked and upper Deschutes. The "blends" of water created by the tower this year tend to be somewhat warmer in spring and early summer than when the dams' only release point was from the depths of the reservoir where the coolest water rests.

Water management officials report that the water 100 miles downstream of the dam at the river's mouth in July were at the high end of the range of temperatures recorded over the previous 10 years, but not out of the range of expectations for that time of year.

Despite the anglers protests about river temperatures being a detriment to the fishery, the steelhead catch in the lower Deschutes was above average, French said. He attributed that to the fact that the number of fish coursing upriver this year is well above average.

"Maybe the two balanced each other out," French said.

Those involved in making sure the Round Butte tower is operated to the specifications outlined in the management plan developed as part of the licensing made a mid-course adjustment in early August.

Oregon Department of Environmental Quality and Warm Springs Tribal Water Control Board officials on Aug. 6, in response to an ODFW request, instructed PGE to increase the amount of cool water to be released down the Deschutes River through the remainder of August.

The planned release for August was to be 30 percent cooler water drawn from the bottom of the reservoir and 70 percent warmer water from near the surface. That mix did not appear to be keeping temperatures consistently lower than the "natural thermal potential" – estimates of what the water temperature would be without the dams in place -- target for that date in August.

The selective water withdrawal tower's first year of operation is considered transitional in terms of temperature management. Not enough cool water has accumulated in the reservoir yet, so blended temperatures are not a cool as they will be with the same percentage of deep water withdrawal in future summers, according to Don Ratliff, a senior PGE biologist.

"It's going to take a little while to dial it in," French said of the need to fine-tune operations. Operations next year should be smoother.

"There will be more cold water carried over from the winter than there has been in the past," said the DEQ's Paul DeVito.

So, for this year it was decided move up the transition to a 40-60 percent ratio of cool water to warmer water that had been scheduled to begin Sept. 1. A shift to 50 percent was scheduled to begin Oct. 1.

The dam operators gradually moved the percentage up from 30 to 40 percent over a 10-day period. The 40-60 percentage ratio will be maintained until about the first of November, when cooler weather will have cooled surface temperatures at Lake Billy Chinook. That means that the same total amount of cool, deep water will be used. But more will be concentrated in the warmer month of August.

Starting in November and throughout the winter, withdrawal will be concentrated from the surface so additional dense cool water can be accumulated through the winter in the bottom of the reservoir to aid water temperature management of the lower Deschutes during the summer of 2011.

There was a bit of a shift in water temperature at the Madras gauge a few miles downstream of the dam from about 59 degrees in early August to a low of 56.6 degrees early this week.

"If you release cold water it gets down to the mouth," French said. The impact is, however, diminished by the time the water flows 100 miles down through high country canyons in the summertime. One estimate is that a cooling of the Round Butte releases by one degree F results in a lowering of the temperature at the river mouth of about one-quarter of a degree.