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Beavers in the South Bay: The Return of a Native Ecosystem Engineer
- Saved By Nature
- 22 hours ago
- 6 min read
North American beavers (Castor canadensis) disappeared from the South Bay for nearly 150 years — until a gnawed tree on the banks of the Guadalupe River changed everything in 2013. This is the backstory of how beavers returned to San Jose's urban waterways, and what their presence means for watershed restoration across the South Bay.
A Wildlife Discovery on the Guadalupe River
Back in 2013, when I was working on the Guadalupe River educating thousands of students about our native Chinook salmon and steelhead rainbow trout, Steve Holmes, Executive Director of 👉🏻 South Bay Clean Creeks Coalition, and Roger Castillo, Executive Director of the 👉🏻 Salmon and Steelhead Restoration Group, stumbled upon a wildlife discovery of the decade. While surveying for fall Chinook salmon, they found a tree on the banks of the ancient Guadalupe River that had been gnawed.
Santa Clara Valley Water District was concerned about beaver being in downtown San Jose, as their dams can cause flooding and damage to homes.
We pointed out that the beaver were living within a multi-million dollar flood control project — if they succeeded in building a dam, the water would overflow into the flood control tunnels — so the district allowed them to stay. There would be no trapping and relocating.
Greg Kerekez from the Urban Wildlife Research Project set up game cameras for monitoring. He noticed a newspaper strap around the mother beaver's waist. We organized night and early morning shifts to try to capture her. After about a week we were finally successful — we cut off the strap and sent her in for a medical checkup before safely releasing her back into the Guadalupe River. Without intervention, she would almost certainly have become another victim of plastic pollution. Please cut your newspaper straps before disposing of them.
150 Years Since Beavers Were Last Seen on the Guadalupe River
We were excited at 👉🏻 Guadalupe River Park Conservancy — historically, it had been 150 years since beaver were last documented on the Guadalupe River. I took initiative to begin educating thousands of people about the beaver and hired Greg Kerekez, who co-taught elementary school field trips with me at the river. I eventually worked with graphic designers at 👉🏻 Wildways Illustrated to create an interpretive display in the visitor center — a life-size recreation of an actual beaver den on Los Gatos Creek that Greg had shown me. We would go on to swim with the beavers.
Where Did the South Bay Beavers Come From?
The question I always get asked is: where did the beaver come from? There are two leading theories.
Theory 1 — Reintroduction Above Lexington Reservoir
In 1992, beavers were reintroduced above Lexington Reservoir in the Santa Cruz Mountains by retired California Department of Fish and Wildlife game wardens. It's possible they have since worked their way down Los Gatos Creek and into the broader South Bay watershed.
Theory 2 — Migration from the Sacramento-San Joaquin River Delta
The other possibility is that they migrated from the Sacramento-San Joaquin River Delta. Although beavers do not live in salt or brackish water, they are capable of swimming through it to reclaim freshwater habitats downstream. Martinez, CA has an established beaver population, supported by an organization called 👉🏻 Worth a Dam, founded by 👉🏻 Heidi Perryman — proof that beavers are actively expanding their range across the Bay Area.
How to Spot Signs of Beavers in the South Bay
You don't need to see a beaver to know one is nearby. Here's what to look for along South Bay creeks and waterways:
Gnawed Sticks and Tree Stumps
The most reliable sign is fresh gnaw marks — sticks with the ends chewed to a point, like a sharpened pencil, and tree trunks with a distinctive hourglass shape at the base. Look for fresh wood chips and pale exposed wood, which indicates recent activity.
Beaver Scat
Beaver scat is cylindrical, fibrous, and woody — typically found submerged at the bottom of shallow water near active feeding or dam sites. The woody debris mixed into the scat is a distinctive identifier.
Beaver Dams and Lodges
Active dams are constructed from branches, mud, and debris packed tightly across a creek channel. Lodges — dome-shaped mounds of sticks rising from the water — indicate a family has established a permanent home.
Why Beavers Matter for South Bay Watershed Restoration
Beavers were nearly hunted to extinction for their fur during the 1800s. Their return to the South Bay is not just a wildlife story — it's an ecosystem restoration story.
Beavers are keystone species and ecosystem engineers. Their dams slow water flow, raise the water table, filter sediment, and create wetland habitat that supports dozens of species. In the past, fishery biologists worried that beaver dams blocked salmon migration — but 👉🏻 a landmark study by Michael M. Pollock, an ecosystems analyst with the 👉🏻 National Oceanic and Atmospheric Administration (NOAA), found the opposite: wild salmon are adept at crossing beaver blockages, and beaver ponds actually create critical rearing habitat and summer holdover spots for salmon, steelhead trout, and sensitive amphibians and reptiles.
As the South Bay faces increasing drought and climate pressure, beavers are a natural ally in watershed restoration — building the slow-water habitat that fish, wildlife, and healthy creek systems depend on.
Frequently Asked Questions About Beavers in the South Bay
Are there beavers in San Jose?
Yes. Beavers were rediscovered on the Guadalupe River in downtown San Jose in 2013 — the first confirmed sighting in approximately 150 years. They have since been documented on Los Gatos Creek and Coyote Creek throughout the South Bay.
Where did South Bay beavers come from?
Two theories exist: beavers reintroduced above Lexington Reservoir in 1992 by retired California Department of Fish and Wildlife game wardens may have migrated downstream via Los Gatos Creek, or they may have spread inland from the Sacramento-San Joaquin River Delta, swimming through brackish water to reach freshwater habitats.
Are beavers native to the South Bay?
Yes. North American beavers (Castor canadensis) are native to California and historically inhabited South Bay waterways including the Guadalupe River. They were eliminated from the region by the fur trade during the 1800s and were absent for approximately 150 years before their return.
How can I spot a beaver in the South Bay?
Look for gnawed sticks with pencil-pointed ends, tree trunks chewed to an hourglass shape, beaver dams across creek channels, and cylindrical woody scat on creek beds. Active gnaw marks show pale fresh wood and are the most reliable indicator of recent beaver presence.
Are South Bay beavers protected?
North American beavers are a native species in California. Santa Clara Valley Water District ultimately allowed the Guadalupe River beavers to remain in place rather than trap and relocate them, recognizing their presence within an existing flood control structure posed manageable risk and significant ecological benefit.
Do beaver dams harm salmon?
Research by NOAA ecosystems analyst Michael M. Pollock shows that wild salmon are capable of crossing beaver dams and that beaver ponds actually benefit salmon and steelhead by creating critical rearing habitat, summer holdover areas, and cooler, deeper water conditions.
Explore South Bay Wildlife With Saved By Nature
The return of beavers to the Guadalupe River, Los Gatos Creek, and Coyote Creek is one of the South Bay's most remarkable urban wildlife stories — and it's still unfolding.
Understanding how keystone species like beavers shape entire ecosystems is at the heart of what Saved By Nature's 👉🏻 outdoor education programs teach: that nature is resilient, that restoration is possible, and that informed communities are essential to making it happen.
Join one of Saved By Nature's 👉🏻 upcoming nature walks along South Bay creeks and waterways to explore the habitats where beavers, salmon, steelhead, and dozens of native species are reclaiming their place in the urban watershed.
Written by Richard Tejeda
Founder & Executive Director of Saved By Nature
SEO, GEO, & Content Optimization by Lyle van Tonder
Digital Marketing Specialist | Web Developer | SBN Board Member
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