Northwest rivers had unseasonably high temperatures this
summer, warm enough to kill thousands of migrating sockeye salmon headed to the
mid-Columbia and lower Snake rivers.
According to a study released by the Fish Passage Center at
the end of October, higher water temperatures in the Columbia and Snake rivers
were largely due to dams and the study particularly points to higher water
temperatures at Bonneville Dam since the four lower Snake River dams were built
in the 1970s. (see page 5 of the study at
“As a result of this review, our overall conclusion is that
elevated water temperatures in the Columbia and Snake rivers, including adult
fishways, is a long-recognized problem that to date remains largely
unmitigated,” the study says. “Significant long-term actions to address these
temperature issues are necessary for the continued survival of salmon
populations, particularly sockeye.”
The study was completed by the FPC staff and sent with a
letter October 28, 2015 by Michele DeHart, director of the FPC, to Charles
Morrill, Washington Department of Fish and Wildlife, Erick VanDyke, Oregon
Department of Fish and Wildlife, and Steven Hawley, citizen. All had requested
similar information from the FPC about why so many sockeye salmon were unable
to finish their spawning migration this summer.
Hawley made the request after reading a Seattle Times
article about the “snow pack drought” that left fish dying in the rivers (see http://www.seattletimes.com/seattle-news/environment/snowpack-drought-has-salmon-dying-in-overheated-rivers/)
The FPC provides technical services to the fish agencies and
tribes impacted by the operation of the Federal Columbia River Power System.
The 2015 migration year for sockeye salmon was especially
damaging for the two fish runs that have been making a comeback in recent
years. NOAA Fisheries at one point in July 2015 estimated that 80 percent to 90
percent of the summer return of sockeye into the Mid-Columbia River were lost.
The run was expected to be nearly a half million fish.
The return of Snake River sockeye, listed as endangered
under the federal Endangered Species Act, was even more dismal. Just 101 fish
returned to Idaho, but only half of those fish swam all the way to Redfish Lake
on their own. The remaining fish were trapped and trucked from Lower Granite
Dam in Washington or the Sawtooth Fish Hatchery on the Salmon River in Idaho.
The study says that building the hydrosystem has had a
significant effect on temperature in the rivers. “By slowing water flow and
increasing surface area for solar radiation, dams caused increased water
temperatures in the reservoirs,” it says.
However, that assessment is not new and FPC says that the
inability to meet water quality standards for temperature was first identified
in the 1995 Biological Opinion for salmon and steelhead in the Columbia/Snake
In 2003, the Environmental Protection Agency began to
develop a temperature Total Maximum Daily Load Limit for the mainstem Columbia
and Snake rivers, but the melding of the TMDL process and NOAA’s BiOp water
quality plan resulted in the TMDL not being finished and so a maximum load
allocation for temperature was never established.
“Despite continued development of Water Quality Plans over
the years, the BiOp process has fallen short of ever really making an impact on
water temperature beyond the actions initially identified in the 1990s,” the
study says. “Over thirty measures were considered to address temperature, but
due to identified issues were dropped from the WQP.”
Here’s what happened in 2015, according to the FPC study:
Spring flows at Lower Granite Dam on the lower Snake River
and at McNary Dam on the mainstem Columbia River were the second lowest since
the 1995 BiOp. Summer flows at Lower Granite were the second lowest since 1995
and the fifth lowest at McNary, also since the BiOp.
Water temperatures at all the Columbia River dams and lower
Snake River dams were higher earlier in the season than at any time in the past
ten years. At nearly all the dams, temperatures exceeded the 20 degree C standard
(68 degrees F) 35 percent to 46 percent of the April to August passage season,
except at Lower Granite Dam which has the advantage of temperature augmentation
from Dworshak Reservoir. Over the previous ten years, the 20 degree C
temperature was exceeded 20 percent to 30 percent of the passage season.
Exceeding the temperature standard in the Snake and Columbia
rivers generally occurs in July and August, but in 2015 it began in late June,
the report added.
Drum gate maintenance at Grand Coulee Dam exacerbated the
low flow conditions beginning in the spring. To complete the maintenance, which
was required this year, the Bureau of Reclamation (the dam’s operator) had to
lower the level of Lake Roosevelt below its April 10 BiOp level and, in effect,
use water earlier that could have been used to augment flows later.
The flow situation in the Columbia River “was somewhat
alleviated by the Columbia River Treaty provision of the proportional draft of
reservoirs under low flow conditions, providing approximately 5 million acre
feet of water from Canadian Reservoirs in 2015,” the report says.
The higher temperatures had a drastic effect on migrating
adult sockeye. According to FPC’s report, higher water temperature cause
migration delays and reduced survival, and that these impacts can occur at
temperatures even lower than 20 degrees C.
It’s not just peak temperatures that impact sockeye, the
report says. It is also likely the cumulative measure of thermal exposure and
that might be a more appropriate way to measure high temperature impacts on
their migration and survival.
In addition, the adult passage ladders past dams “often
exhibit temperature gradients because the water sources differ throughout the
ladder.” Temperature gradients greater than 1 degree C can significantly delay
migration to spawning grounds, increase total thermal exposure, deplete the
fishes’ energy resources and decrease migration success, according to the
While there has been some hope of cooling fishways at lower
Little Goose and Lower Granite dams by using auxiliary pumps to put cooler
water into them, the report says that likely would not have helped in 2015
since most of the adult migrants already had died farther downstream.
These conditions profoundly impacted sockeye passage, travel
time and survival. The 2009 to 2014 migration years saw survival of adult
sockeye from Bonneville Dam to Lower Granite Dam of 44 percent to 77 percent.
In 2015, survival was just 4 percent, the report says. Snake River sockeye that
had been transported as juveniles had even lower survival rates and they had a
higher fallback rate at Bonneville than in-river fish.
Survival of upper Columbia River sockeye in 2015, Bonneville
to Rock Island Dam, was 46 percent, the lowest among the years 2009 to 2015.
Migration times in 2015 increased over the past six years as
river temperatures rose, the report says.
For more information on warm water issues during 2015 salmon
-- CBB, September 11, 2015, “Snake River Sockeye: Lowest
Return Since 2007, Captive Broodstock Program Increases Spawners,” http://www.cbbulletin.com/434944.aspx
-- CBB, August 28, 2015, “Smoke, Lower Air Temperatures Keep
Lower Snake Cooler; 33 Sockeye Make It To Redfish Lake Trap” http://www.cbbulletin.com/434826.aspx
-- CBB, July 31, 2015, “Warm Water Hitting Returning Sockeye
Hard: NOAA Says Maybe 80 Percent Mortality For Upper Columbia,” http://www.cbbulletin.com/434644.aspx
-- CBB, July 24, 2015, “Finding Water For Columbia River
Fish In A Low Flow Year; Most Comes From Canada Storage Reservoirs” http://www.cbbulletin.com/434590.aspx
-- CBB, July 17, 2015, “Snake River Sockeye Trapped,
Transported At Lower Granite; ‘Fish Are Stressed And In Rough Condition” http://www.cbbulletin.com/434539.aspx
-- CBB, July 10, 2015, “Lower Granite Water Temps Go Above
68 Degrees; Returning Snake River Sockeye Stalling Through System” http://www.cbbulletin.com/434488.aspx
-- CBB, June 26, 2015, “Hot Weather Forces Dworshak Flow
Increase To Cool Lower Snake; Snake River Sockeye Passing Bonneville” http://www.cbbulletin.com/434342.aspx
-- CBB, June 19, 2015, “Water Temps (near 68), Lower Flows
Prompt Earlier Than Usual Summer Hydro Operations In Lower Snake” http://www.cbbulletin.com/434289.aspx