California Forum

Hard work, smart science contribute to salmon’s success on Cosumnes River

Restoring and maintaining salmon in the wild, dam-free Cosumnes is a unique opportunity.
Restoring and maintaining salmon in the wild, dam-free Cosumnes is a unique opportunity. Sacramento Bee file

For a respite from holiday pressures – or the news – pause and take a moment to visualize large silver-pink fish dancing upstream against the current of a wild river toward their historic spawning gravels. The Cosumnes River, the natural jewel on Sacramento’s southern flank, is enjoying its best run of Chinook salmon in years.

The count so far is impressive, upward of a thousand. Their journey from the ocean toward the mountains is measured by a device mounted above a fish ladder that counts and photographs fish as they follow their ancient genetic drive.

This year’s Cosumnes salmon are a mix of fish bred in hatcheries and fish propagated in the wild. All that are fit enough to survive the arduous process of hatching in the wild will spend the remaining years of their life in the ocean before they return to the Cosumnes to spawn and pass on their genetic material to the next generation.

For the San Joaquin River system as a whole, natural salmon production means more genetic diversity and reduced vulnerability to disease, factors crucial to the long-term survival of the species. Restoring and maintaining salmon in the wild, dam-free Cosumnes is a unique opportunity.

The Cosumnes is without dams by accident. Efforts over generations to build a dam were frustrated by the relatively small size of the watershed and the cost of any reservoir relative to yield. Federal dam-builders gave up in the 1970s, leaving the Cosumnes, unique among Sierra rivers, with a natural flow profile.

And this year’s strong salmon run is due in part to luck – strong fall rainstorms that brought flow to the river in early October. In most years, fall river flows needed by fish go underground because of groundwater overdraft.

But hard work and smart science are equally important factors. Investments by public agencies and nonprofit organizations began in the 1980s, led by the U.S. Bureau of Land Management and The Nature Conservancy in the lower watershed, and by the American River Conservancy in the upper watershed. The 1990s witnessed substantial progress in protecting watersheds and restoring natural floodplains in the lower watershed, areas essential for juvenile salmon.

More recently, a collaboration led by the Fishery Foundation systematically renovated historic diversion structures along the lower Cosumnes, eliminating barriers to fish passage. The foundation received funding from the federal Anadromous Fish Restoration Program and completed the work in 2011.

The past few decades of progress for the watershed resulted from close collaboration among often divergent interests: farmers, conservation organizations, and government agencies. The salmon are telling us we are on track.

But as 2016 closes, the fish still face serious threats: climate change, projected to make extended droughts more frequent; increased diversions, both legal and illegal, in the upper watershed; and groundwater overdraft. Continuing smart investments in conservation, good science and new technologies will help, as will the state’s new groundwater law.

Fortunately, once again agricultural landowners, agencies, nonprofits and academic partners UC and Sacramento State have accepted the challenge and are developing innovative projects that mimic natural processes to address the flow challenges.

Salmon were central to the lives and the worldview of the Miwok people, stewards of the river and its watershed for the millennia preceding the Gold Rush. That intimacy is mirrored in their name for the river itself: “Cos” means salmon and “umne” means people. The Miwok knew, as we have learned, that a living watershed needs salmon and a healthy watershed produces salmon.

Let’s honor that fundamental reciprocity by assuring there will be reason to celebrate every fall.

Mike Eaton worked for The Nature Conservancy from 1995 through 2007 and now advises the Cosumnes Coalition, a watershed restoration partnership. Contact him at