The Golf Course Dam Nearly Killed the Salmon Run. Now the Same Spot Is Where to Watch It Return.

How does a creek covering roughly a tenth of a watershed end up carrying close to half its endangered salmon run?

That is the actual story of San Geronimo Creek, the stretch of water that runs behind Woodacre, Forest Knolls, San Geronimo, and Lagunitas before it joins the larger Lagunitas Creek on its way to Tomales Bay. The Lagunitas Creek watershed covers about 60,000 acres and holds the largest remaining wild run of coho salmon on the central California coast. San Geronimo Creek drains only about 6,000 of those acres. Depending on the year, biologists estimate this one tributary still accounts for somewhere between a fifth and two-fifths of all the coho spawning that happens across the entire system, and as much as a third of the young salmon born into the watershed spend their whole freshwater lives right here before heading to the ocean.

That is a strange amount of ecological weight for one small side creek to carry, and the reason has almost nothing to do with the creek itself. It has to do with a dam, a golf course, and one biologist who happened to be paying attention in 1997.

The Dam That Almost Ended the Story

Before it was anything else, the ground along San Geronimo Creek was a golf course. A low dam called Roy's Dam sat on the creek, built in the 1920s to supply water to a ranch. By the time biologist Todd Steiner went looking in 1997, that dam had become something else entirely: a wall. Coho salmon returning from the ocean to spawn were getting stuck below it, unable to climb over to reach the gravel beds upstream where they needed to lay their eggs.

Steiner brought the problem to the media and to federal wildlife regulators, pushing for an emergency permit to move the trapped fish above the obstruction. That fight became the founding moment of the Salmon Protection and Watershed Network, known locally as SPAWN, which has spent the years since working to protect this exact stretch of creek and the fish that depend on it. Rather than remove Roy's Dam outright, engineers chose to lower it, since so much sediment had built up behind it that full removal risked burying the creek downstream. The lowered structure reopened spawning habitat that had been cut off for decades.

The golf course itself is gone now, replaced by San Geronimo Commons, a public open space where the creek section near the old dam site is known today as Roy's Riffles. Restoration work there has continued in stages over the past several years, and creek habitat is one of several projects still moving forward on the property, alongside separate efforts covering flood protection and trail connections, as B.G. Bates covered in a recent look at the Commons. The short version for anyone who has not been following along: the fairways are gone, but the creek that runs through them is doing more conservation work than most protected land twice its size.

What Last Winter's Numbers Actually Looked Like

The 2025-26 water year gave a good preview of what that work looks like in practice. Rain arrived early, starting in September 2025, and by mid-November over nine inches had fallen. Stream flows in Lagunitas Creek rose above 100 cubic feet per second on three separate occasions that fall, unusually early conditions that gave salmon a head start on their migration.

Chinook salmon are typically the first species to show up each season, and this year they took full advantage. Marin Water's fisheries crew counted 149 Chinook in a single day on November 12, 2025, a record for that species in the watershed. The following week brought roughly 70 more Chinook in the short stretch between the Leo T. Cronin Fish Viewing Area and Peters Dam, and more than 50 Chinook were counted in San Geronimo Creek itself, all the way up to Woodacre. That is not a generic waterway a mile from town. That is fish swimming past the edge of the village.

Coho followed, with more than 100 observed moving upstream by that same point in the season, though most were still holding in deep pools waiting for additional rain rather than spawning outright. Coho need fast-moving water to dig their redds, the gravel nests where they lay eggs, and Marin Water's own forecast for the season put the total coho run at around 400 fish, smaller than a typical year but roughly double the size of the parent generation that spawned three years earlier. That distinction matters here because coho live on a strict three-year cycle, so each year's run is really being measured against the specific class of fish that produced it, not against some flat historical average.

None of this happened at a nature preserve somebody built for the purpose. It happened in a creek that runs behind people's back fences.

Where Residents Actually Go to Watch

The season generally runs from October through April, with the most dramatic activity, fish visibly thrashing upstream in ones and twos, concentrated in December and January. A handful of specific spots account for most of what people see.

Roy's Riffles is worth singling out. It is the only spot on this list that did not reliably hold spawning fish a generation ago, and the reason it does now is entirely due to the dam decision made decades back and the restoration work since.

The Guided Walks, If You Want Company

SPAWN has led public Creekwalk Tours along this watershed for more than 20 years, typically on Saturdays through December and January with a few added dates around the holidays. The organization trains a new group of volunteer naturalists every October, so by the time the rains bring the first fish upstream, the guides leading those Saturday walks are already prepared for the season. Tours run rain or shine, since wet days often produce the best viewing, and cover one to two miles combined across the various sites. A $15 donation per person is suggested, children 12 and under go free, and private tours can be arranged for a $200 donation or in exchange for a volunteer restoration shift.

For anyone who wants the raw data instead of a guided walk, Marin Water maintains a public Spawner Dashboard with more than two decades of salmon and steelhead counts and redd locations going back to 1999. It is the same dataset the fisheries crew uses to track the season in real time, and it is open for anyone to look up.

Why This Matters Beyond the Fish

The Central California Coast coho population overall has fallen from a historic estimate in the tens of thousands of returning adults to an average of around 500 a year in recent decades, with some years as low as 67. Against that backdrop, a small tributary that still produces a disproportionate share of the watershed's spawning and rearing habitat is not a minor local curiosity. It is one of the more functional pieces of habitat left for an endangered species on this stretch of coast, and it happens to run through the middle of a residential valley.

That is the part worth sitting with if you live along San Geronimo Creek. The restoration work at the Commons is not finished, and the creek's role in the broader watershed is not static. It shifted once already because one person noticed fish stuck behind a dam on a golf course and refused to let it go. It can keep shifting, for better or worse, depending on what happens to the banks, the flow, and the ground around it in the years ahead.

If you want to see what that looks like in practice this winter, the creek will tell you. Watch for the first Chinook once the fall rains settle in, usually by November, and for the coho to follow once the water runs fast enough for them to dig. Roy's Riffles is as good a place as any to start, and it is a short walk from wherever you already are.

If you are thinking about your own place in this valley, or wondering what a home near this stretch of creek is actually worth given everything happening on the land around it, B.G. Bates has spent years tracking West Marin's water, land, and conservation questions alongside its real estate. Begin your West Marin story and reach out anytime.