The deaths of at least 21 juvenile steelhead trout and the stranding of 150 in puddles following a drop in water levels in the west fork of the Russian River near Redwood Valley has focused new attention on farm practices.
The fish kill — discovered April 28 — coincided with farmers drawing water to spray for frost protection, adding fuel to federal fisheries officials' contention that the practice needs to be strictly regulated to protect endangered and threatened species.
"This incident illustrates that voluntary efforts have not prevented frost diversion-related fish kills and confirms the need to regulate water use," said Dan Torquemada, assistant special agent in charge with the National Oceanic and Atmospheric Administration's law enforcement office.
Mendocino County farmers, primarily grape growers, and water officials disputed Torquemada's conclusion, citing data from a U.S. Geologic Survey gauge on the river in Redwood Valley that they say did not show a significant drop in flows.
The river level dropped just under 1 centimeter during the eight hour period beginning just before midnight the day before the fish were discovered, said Sean White, a fisheries biologist and director of the Mendocino County Russian River Flood Control and Water Conservation Improvement District.
More dramatic was a 5-inch drop in the depth in the 12 days prior to the discovery of the stranded fish, he said.
"The major impact is from the west fork drying up from warm days and no rain," White said.
The west fork of the Russian River normally dries up once the rains stop because, unlike the main stem, it is not fed by releases from Lake Mendocino, the reservoir behind Coyote Dam north of Ukiah.
Farmers and local, state and federal water and fisheries officials have been locked in a three-year debate over how best to prevent fish from being killed when grape growers pump water from the river and its tributaries.
The debate began in 2008 when threatened and endangered fish in the Russian River in Sonoma and Mendocino counties were stranded and died, apparently as the result of too many farmers taking water at once. Another incident was reported in Sonoma County in 2009.
Sate officials have warned that they will impose regulations that include prohibiting diversions for frost protection from March 15 through May 15 in the absence of an acceptable local river management plan.
But the factions are having difficulty agreeing. Farmers prefer voluntary methods while some federal officials have suggested a ban on use of river water for frost protection. In Sonoma County, a proposed ordinance was scuttled in part by objections from some growers who did not want to report how much water they take from the river.
White recently told officials at a Sacramento frost protection meeting that he didn't think their proposed regulations would result in more water in the streams.
There also is disagreement about the magnitude of the problem.
Federal fisheries officials estimate that frost protection killed 25,000 fish near Hopland in 2008. White said that estimate is ludicrous because it's based on finding about 10 dead fish.
"There's no evidence supporting beyond 10," he said.
Fisheries officials have not estimated how many fish may have died this time, but they believe it's many times more than the 21 they found, Torquemada said.