Small Dam, Big Deal: York Dam Removed in Napa Valley

By: Amber Manfree, Peter Moyle, Ted Grantham

Former Site of York Dam and reservoir, now an engineered channel allowing fish passage, September 2020. Photo by Amber Manfree

The recent removal of the sediment-filled York Dam in Napa County has reconnected two miles of steelhead trout habitat that has been blocked for over a century. While the dam itself was small and non-functional, it took nearly 30 years to accomplish removal. Thousands of barriers to stream flow and fish passage similar in size and impact to York Dam are scattered throughout California, contributing to population declines in native fishes and other freshwater species. Reconnecting streams will help counter climate change impacts, allowing fishes access to more habitat for spawning and rearing. Completion of the York Dam removal project is encouraging, and it shows us what can go wrong – and right – at the local level.

California’s inland waterways have thousands of dams that store water for use by people. The dams that usually come to mind are giant concrete structures central to our water supply system such as Shasta, Oroville, and New Don Pedro dams. These are among the 1,400 or so dams monitored by the state because they are big enough to threaten human safety if they fail. But these so-called jurisdictional dams only represent a fraction of the total number of dams that exist in our state. There are thousands smaller dams as well. It is a rare watershed of any size that lacks a dam.

In the Napa River watershed, there are 37 jurisdictional dams, an additional 27 non-jurisdictional dams that block fish passage, and dozens more in-stream dams high up in watersheds that block flow, but not passage (see The Refugia Project). In total, over 60,000 acres, or 23%, of the watershed is behind dams.

Dams blocking fish passage in the Napa River watershed. Graphic by Amber Manfree

Regardless of size, all dams share some important characteristics:

  • They have a finite life span: Dams are not built to last forever and most are designed with an expected life span of less than 100 years. Eventually dams must be replaced or removed – naturally or by human means. What goes up, must come down.
  • Their useful life is shorter than their physical life: Dams are designed to store water, but they also collect and store sediment washed down from the watershed into the reservoir and trapped. Over time, dams fill up with sediment and can no longer store much water. This process is being accelerated by recent fires in the Napa River watershed and throughout the state.
  • Dams negatively impact freshwater ecosystems. For example, dams alter the physical dynamics of streams including the movement of water, sediment, and organisms through the river networks. These changes in turn modify aquatic and riparian biota and critical ecological processes. Dams are a primary driver of salmon population declines because they block fish migration and alter natural patterns of flow downstream.

If removal of defunct dams were easy, there would not be so many of them. The story of York Dam on York Creek, a small tributary to the Napa River near St. Helena, provides an example of how challenging removal can be. York Dam was constructed by Chinese laborers in the 1870s, as an earthen dam 24 feet high and 225 feet long, completely blocking migratory steelhead from accessing the upper reaches of York Creek. The dam was designed to provide water to the City of St. Helena and local wineries, and was owned by the City. The dam did its job for decades, although the pool behind it gradually filled with sediment, reducing water deliveries. Eventually, the dam completely filled with sediment and provided no beneficial functions. The site fell into a state of disrepair. A small redwood forest grew on the dam’s earthen face and willows took root in the sediment that accumulated behind it.

Winter flows from base of York Dam prior to dam removal, January 2017. Photo by Amber Manfree

In 1992, an uncontrolled sediment spill from York Dam caught the attention of the California Department of Fish and Game (now Fish and Wildlife; CDFW). A court order was obtained to require St. Helena to remove the dam and the silt accumulated behind it, but no work was done. In 1997, the Central California Coast steelhead, a major beneficiary of dam removal, was listed by the National Marine Fisheries Service as a Threatened species, a status upheld in 2006 and 2014. Although there are two miles of steelhead spawning and rearing habitat above the dam that could contribute to species recovery, still no action was taken. Then in 2012, the court order was lifted on the understanding that the City would pursue removal with grant funding that had been obtained for that purpose. The National Marine Fisheries Service (NMFS) imposed a fine of $70 per day until proper action was taken. Still nothing happened, and the total penalty rose to over $190,000 by 2020.

Steelhead habitat upstream of York Dam, July 2020. Photo by Amber Manfree

The failure to act was finally overcome after Water Audit California, a Public Benefit Corporation, threatened to sue the City to take down the dam, citing violations of the California Fish & Game Code and the Public Trust Doctrine. Negotiations led to a settlement in which the City of St. Helena agreed to remove the dam and Water Audit agreed to defer legal action, conditioned on the City’s performance. With the full involvement of NMFS, CDFW, the US Army Corps of Engineers, representatives of indigenous people and other interested parties, a process of removal was approved.

In September, 2020, the removal of York Dam was completed, restoring unimpaired flows to the creek for the first time in 150 years. Part of the agreement was to use trees cut from the face of the dam to create habitat structures in the creek. The Glass Fire swept through the area in early October, and its effects on the creek and the new structures are not yet fully understood. This new challenge will provide an opportunity to see if the cooperative process that resulted in dam removal will lead to future actions to manage stream habitat in York Creek.

York Dam removal site looking downstream after the Glass Fire, October 2020. Photo by Amber Manfree

The removal of York dam is among a number of recent successes led by Water Audit to restore Napa Valley creeks, including new agreements with dam operators to improve flows in Rector, Kimball, and Bell Canyon creeks. Water Audit has also undertaken The Refugia Project, a comprehensive review of the Napa watershed encompassing stream flow and obstructions, water quality and groundwater withdrawals. The project is supporting initiatives to remove streambed obstructions, to open additional spawning reaches to steelhead, to measure surface water flows and quality, and to model the effects of groundwater extraction on river flows.

Such efforts are the start of restoration of the Napa River watershed as a place where steelhead and other native fishes thrive. The removal of York Dam is just one of many projects needed to restore fish and flows to Napa Valley creeks and to improve the ecological health of the Napa River itself.

As a locally owned structure, the fate of York Dam ultimately rested on local leadership, and there are lessons to draw from the 30-year delay in action. The current mayor of St. Helena, Geoff Ellsworth, collaborated in the final push to remove York Dam, avoiding further legal action. He says, “For these legacy environmental projects to move forward they must be recognized by the council and community as critical to keep at the top of the queue in terms of priority, preparation, and set up.” Ellsworth acknowledges that keeping the administrative process moving requires active leadership, adding  “A consistent political will and dialogue needs to be fostered in elected officials, as well as building a culture of staff retention so projects like this don’t accidentally fall through the cracks or get put on a back burner.”

Given that most dams in California were built in the last century, many are no longer functional or provide limited benefits to people. Non-functioning dams should be removed in a safe, planned manner, before they fail on their own. At the very least, obsolete projects should be modified to limit their impacts to fish and wildlife habitat. In order to responsibly manage resources, every dam in the watershed – and indeed in the state – should be evaluated for its life span, utility, public health risks, and its effects on native fishes to ensure a better future for both fish and people who live there. Logistically, this will involve consistent pressure from advocacy groups, occasional legal nudges, and – most importantly – follow-through from administrators and officials to set projects into motion.

Dams and dammed watersheds in California. Graphic by Amber Manfree

Amber Manfree has a PhD in Geography from UC Davis and is a consultant to Water Audit on the Napa Watershed.  Peter Moyle is a professor emeritus of fish biology at UC Davis. Ted Grantham is an UC Cooperative Extension Specialist at UC Berkeley.

Further Reading

Rypel, A.L., C.A. Parisek, J. Lund, A. Willis, P.B. Moyle, Yarnell, S., and K. Börk. 2020. What’s the dam problem with deadbeat dams?,

About Andrew Rypel

Andrew L. Rypel is a Professor and the Peter B. Moyle and California Trout Chair of coldwater fish ecology at the University of California, Davis. He is a faculty member in the Department of Wildlife, Fish & Conservation Biology and Director of the Center for Watershed Sciences.
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1 Response to Small Dam, Big Deal: York Dam Removed in Napa Valley

  1. Jeff says:

    Dams to store water are a direct result of human overpopulation. Before Europeans overpopulated, they lived off local ground water. The California Natives, who were not overpopulated, lived solely off of surface water, which is even better and the only way to get water that’s not at least somewhat ecologically destructive. People need to start addressing overpopulation by lowering their family size, or these problems will only get worse.

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