While Glen Canyon Dam’s impacts on the ecosystem at Grand Canyon are well-documented, less publicized are the impacts that Lake Powell reservoir has on critical habitat upstream. Nowhere is this more apparent than on the San Juan River where 20 percent of the habitat has been inundated by the reservoir. The Bureau of Reclamation (BuRec) claims it can remedy these problems by re-operating Navajo Dam upstream, but Living Rivers is leading the effort to reinforce how futile this exercise has been, and will continue to be, until Lake Powell reservoir is drained.
The San Juan River is well-known for contributing about a third of the sediment that historically nourished the lower Colorado River system and its delta. The 355 mile long San Juan River is also one of the most unique ecosystems on the planet, supporting an incredible diversity of endemic plants and animals, as well as native cultures. But, like so many rivers in the Colorado watershed and beyond, the San Juan has suffered tremendously as a result of dams and water diversions.
Of the six native fish species that once thrived in the San Juan, four are species of "special concern," and two are threatened with extirpation. Under pressure from the Fish and Wildlife Service, BuRec has been studying ways to modify the operations of its Navajo Dam facility to improve San Juan River habitat conditions for the endangered Colorado Pikeminnow and the Razorback Sucker. Located 208 miles upstream from where the San Juan River becomes part of Lake Powell reservoir, it is believed that changes in dam operations could bring about the recovery of these native fish.
But, as was acknowledged in a recent Environmental Impact Statement on the operations of Navajo Dam, such flow regimes have yet to achieve a "positive population response." In fact, scientists have concluded that there has been little to no benefit whatsoever to the endangered fish populations as a result of present dam operations. Nonetheless, BuRec recommends continuing with the same regime.
"The problem is they’re looking in the wrong direction," says Living Rivers conservation director John Weisheit. "The major constraint is not the need to manipulate flows, but to recognize that the remaining stretch of river is too short to allow for young fish survival."
Historic habitat for the native San Juan River fish included the spawning beds above Navajo Dam and the rearing sections now inundated by Lake Powell reservoir. Navajo Dam, Glen Canyon Dam and the nine diversion dams in between, have reduced river habitat down to 81 miles (a loss of 75 percent). While it has been demonstrated that spawning habitat is available for the fish, the important rearing habitat for young fish is insufficient. Hatchlings drift into Lake Powell reservoir and are consumed by non-native fish before they have sufficiently matured to swim upstream against the current.
Historically, the native fish of the San Juan River could rely on the free-flowing Colorado through Glen Canyon to provide both rearing habitat and refuge habitat when the San Juan River ran dry. Decommissioning Glen Canyon Dam would restore the historic geomorphic habitat that the fish evolved with, as well as increase the range and conditions of critical habitat necessary for the recovery of these incredible fish.
"BuRec is completely ignoring these rearing habitat constraints and the role a decommissioned Glen Canyon Dam must play in eliminating them," adds Weisheit. "BuRec must stop wasting public monies pretending. They must concede that this remaining habitat is not sufficient to support recovery, and that they will be in violation of the Endangered Species Act until Lake Powell is drained."
