Water diversion gates in the Sacramento-San Joaquin Delta near Walnut Grove will not be closed this month to assist migrating salmon, as they were last year.
The Delta Cross Channel Gates, operated by the U.S. Bureau of Reclamation, were built in 1953.
They are typically open in fall to divert fresh water from the Sacramento River to the interior of the Sacramento-San Joaquin Delta. This reduces the salinity of water exported from the Delta for urban and farm use.
In recent years, concern has emerged that salmon migrating upstream to spawn in the Mokelumne River are disoriented by flows diverted through the gates and often end up spawning in the wrong stream. So the gates were closed last year for 10 days in October, which may have contributed to a rebound in salmon production at the Mokelumne River Hatchery, operated by the state Department of Fish and Game.
This year the gates will not be closed, said Sue Fry, manager of Reclamation's Bay-Delta Office.
Doing so would cause salinity intruding from San Francisco Bay to increase significantly, likely violating a state water quality standard, she said. One reason is that it has been a dry water year, so there isn't enough freshwater outflow to control salinity.
Reclamation is required by Endangered Species Act rules to close the gates when a certain number of salmon are detected at upstream monitoring sites on the Sacramento River, which has not yet occurred. Even so, water-quality standards must still be met.
"We want to try to help those Mokelumne River fish not to stray," Fry said. "This is something Reclamation will look at every year to lend information to studies that are ongoing."
Reclamation announced Friday it is launching a five-year study, using tagged salmon, to assess whether closing the gates actually helps fish. Closure in these study years will, once again, depend on water quality conditions.
Dick Pool, a board member of the Golden Gate Salmon Association, said missing the gate closure this year is troubling because Mokelumne River is an important producer of salmon later caught as adults in the ocean by commercial fishermen.
"We are concerned and are going to try to pull out all the stops to keep this from happening next year," Pool said.
For more information on the U.S. Bureau of Reclamation study, visit http://ht.ly/eFZUi