Low river flows hampering fish
Low streamflows are forcing dam operators to choose between irrigation and fish—and at some sites are taking the decision out of their hands.
Endangered and other native fish may pay a price this summer, but wildlife officials are hopeful that as long as the drought does not last multiple years, fish populations will not be affected in the long term.
Though the drought-hardy fish are no strangers to occasional low flows, this year’s flows are exceptional even by their standards—and trying to swim over a wall is a different challenge altogether.
The diversion dams that channel water out of the Colorado and Gunnison rivers to irrigate Grand Valley fields and orchards have historically posed a significant roadblock to fish trying to swim upstream after coming down to spawn in the spring or summer.
But fish ladders built at the four dams over the past 15 years now allow migrating fish, including endangered species such as Colorado pikeminnow and razorback chub, to circumvent the dams.
This year, however, it appears many of those fish will be out of luck.
On Thursday, the fish ladder at Redlands Water and Power Co.‘s dam on the Gunnison just south of Grand Junction was the only one of the four ladders in operation.
The three Colorado River ladders were not operating, and it was not clear when this summer they would be operating again, if at all.
Friday, however, at least one of those ladders, at the Price-Stubb diversion dam, had enough water running over it. That followed a release of about 450 cubic feet per second from upstream reservoirs as part an agreement on the Shoshone Outage Protocol, which is meant to send some water down the Colorado even when the Shoshone power plant — and its senior water right — is down for maintenance.
The Price-Stubb dam’s fish ladder was above the reach of the meager streamflows on Thursday, and it was not clear Friday whether the new water releases would be enough to keep water going over that and other ladders throughout the summer.
“There may be days when it looks like they’re running well, but two days later we may see a drop in river levels,” said Dale Ryden, a fish biologist with the U.S. Fish and Wildlife Service’s Grand Junction office. He noted that evaporation and more absorption into the dry ground may mean less of that water makes it downstream on some days.
“Everybody is on a learning curve because we really haven’t seen levels this low before,” he said. “But we’re all going to be a lot smarter after this year.”
Downstream of Price-Stubb, the Grand Valley Irrigation Co. diversion ladder was taken out of operation earlier this week because of low flows.
And upstream of both of those, the fish ladder at the Grand Valley Project diversion dam south of DeBeque is not going to be in operation at all this summer as there is not enough water for both the irrigation canal there and the fish ladder, Ryden said.
It likely would not make much of a difference if it were operating, though, because passages around the two dams downstream of it are not operating anyway, meaning fish migrating upstream are unlikely to get to the Grand Valley Project.
That ladder is run by the U.S. Fish and Wildlife Service; the other three are run by the irrigation districts that maintain their respective dams.
Richard Proctor, superintendent of the Grand Valley Water Users Association, which operates the Grand Valley Project diversion, said the fish screen that keeps fish and debris out of the irrigation canal also was removed Thursday because “it became apparent we couldn’t get enough water to irrigators” while also leaving the screen in operation.
“We’re struggling to keep enough water going to our irrigators, to people who make their livelihoods off the land,” Proctor said. “This drought isn’t user-friendly.”
Fish heading up the Gunnison will be luckier than those on the Colorado. The Redlands dam was shut down for five days last month—the first time it had ever been down—after exceptionally low flows left the Redlands Water and Power Co. with less water than it needed to operate the hydroelectric-powered pumps that bring water up to Redlands irrigators.
Flows have since climbed back to around 1,000 cfs, still far less than the hundred-year median of around 7,000 cfs for this time of year, but enough for both the irrigation canal and fish passage to have enough water, according to Ryden.
He said the decision that there was enough for both people and fish was made during that five-day window and was facilitated in large part by a Bureau of Reclamation decision to release more water from the Aspinall Unit dams above Black Canyon of the Gunnison National Park to benefit fish downstream.
“The problem with making those paper statements is it sounds wonderful until someone needs that extra 10 or 20 cfs, which is what happened this year” and officials find the amount they expected to have downstream is not there because of leakages or other unforeseen issues, Ryden explained.
But this time, he said, the math turned out to be right.
“We’re actually very close to where we thought we’d be.”
He said the Redlands dam’s fish ladder should stay running through August, at which point it would depend on how much water irrigators need late in the season. Most endangered fish should be back upstream by then, anyway.
The Redlands fish ladder is unique from the Colorado River ladders in that there is a trap in which the fish passing by the dam are temporarily caught. A Fish and Wildlife biologist then sorts through them once a day, letting the native fish pass upstream and tossing the non-natives back below the dam.
This results in a very healthy environment for native fish north of the dam, Ryden said.
RECOVERY ON PAUSE
Non-native fish can pose an especially harmful threat to endangered natives during drought years, when warmer water temperatures and less competition for food from native species mean a more successful spawning season for natives.
Conversely, endangered fish generally have a harder time finding suitable spawning habitat during low-flow years and, if they do spawn, their young are more likely to be eaten by the flourishing non-natives—particularly, in the Grand Valley, smallmouth bass.
Removing those non-natives and building fish ladders are two of the measures of an ongoing project to encourage the recovery of the Upper Colorado Basin’s endangered fish.
Those recoveries are expected to generally be on pause as the rivers reach near-record lows and many endangered fish have trouble spawning successfully.
Instead, the strategy will be to simply minimize damage and hope for a better year next year.
“Given the circumstances, we really just have to focus on removing non-native fish this year, which tend to explode in these low-flow years,” said Tom Czapla, a biologist with the Upper Colorado Endangered Fish Recovery Program, a partnership of government, water users and conservationists working to boost the endangered fish populations.
Ryden is hopeful that 2012 would prove less harmful for the fish than 2002 because reservoirs are much higher now than they were then and more agreements are in place to help get endangered fish the water they need.
“Even though it looks really grim, we’re actually in a better place now,” he said.
What remains to be seen is what conditions will be like next year. Endangered fish populations are expected to be able to withstand one year of low flows, but multiple drought years—and thus multiple years of little spawning—could prove disastrous.
This article is part of a grant-funded project in cooperation with Colorado Mesa University to report on issues of environmental concern.