Status of water supply and water temperature for the successful spawning of returning salmon

(October 19, 2017)

The American River Group and the Bureau of Reclamation reached an tentative agreement to decrease the temperature of the water flowing from Folsom/Nimbus for the benefit of spawning Chinook salmon which have begun arriving earlier than usual this year at the Nimbus Hatchery.  At the end of a good water year, with plentiful storage, you might think that issues like this would take care of themselves, but nothing is so simple.

During the depths of the drought, three years ago, water conditions in the Sacramento River became so lethal that the Coleman National Fish Hatchery on Battle Creek, which services the big chinook salmon run on the Sacramento below Shasta Dam, took the desperate step of trucking their young fish and releasing them directly into San Francisco Bay.  Three years hence, the survivors of that “migration” are returning to fresh water to spawn, but many of them are showing up in the American River this October because they have not had the benefit of imprinting the unique molecular characteristics of their natural spawning waters, the Sacramento River and Battle Creek.

So Nimbus Fish Hatchery finds itself open for business about three weeks or a month earlier than usual, servicing the spawn of Coleman salmon.  The fish can be identified as Coleman salmon and their hatch will be trucked up to their hatchery of origin, but the consequences of all this means that Folsom Dam operators are being asked to lower the temperatures of the water flowing into the lower American about three weeks sooner than they would if they were dealing only with later-arriving Nimbus-spawned chinook.

Water leaving Folsom Dam currently is about 62 degrees — too warm for most successful spawning and rearing.  Ideally, fisheries biologists would want the water temperature below Folsom to be 58 degrees.  The people operating Folsom Dam, however, say that even with this good water supply, they have only enough remaining cold water to maintain the 58 degrees for about 13 days, a circumstance that would benefit the Coleman visitors but jeopardize the success of the Nimbus-spawned migration.

Thursday, fisheries biologists from state and federal agencies settled for 60 degrees, which means that the cold water supply will last into the second or third week of November, according to the Bureau of Reclamation.  Nobody seemed to be quite sure how 60-degree water will affect the success of the Coleman or the Nimbus migrations, although everybody seemed to be sure that it was better for them than 62 degrees.