Santa Margarita River Watershed
One of the last major rivers in Southern California without a single dam on its mainstem — held back from full reconnection by one aging bridge CalTrout is about to replace.
Understanding the WATERSHED
The Santa Margarita River begins near Temecula, where two tributaries converge — and flows 29 miles to the Pacific without meeting a single dam.
The Santa Margarita River watershed is the second largest river basin in Southern California, collecting water from 742 square miles of remote backcountry mountains. The river flows 29 miles from its headwaters through a steep gorge and into broad floodplains before crossing U.S. Marine Corps Base Camp Pendleton and reaching the Pacific Ocean near Oceanside. It is one of the last major perennial rivers in Southern California with no dams on its mainstem — a rare, largely free-flowing system in a region where nearly every river has been reshaped by concrete.
That distinction, protected in large part by Camp Pendleton’s undeveloped lands, The Wildlands Conservancy’s Santa Margarita River Preserve, and San Diego State University’s Santa Margarita Ecological Reserve, has made the watershed one of the highest-priority rivers in the state for steelhead recovery. Southern steelhead once moved freely through this system, migrating from the Pacific up into the cold headwater tributaries to spawn. Today, that run is virtually gone.
Sandia Creek Drive BRIDGE
A single aging concrete crossing on the Santa Margarita River mainstem creates a chokepoint, blocking steelhead from more than 12 miles of high-quality spawning and rearing habitat upstream.
Part 1 | Bridge Replacement Project
A Fish Passage Project Decades in the Making
CalTrout is set to begin construction on the Santa Margarita River Bridge Replacement Project — a critical fish passage project years in the making. The 435-foot steel replacement bridge will reopen a key wildlife corridor, freeing the first Southern California river from headwaters to the ocean, and providing a unique chance at recovery for endangered Southern steelhead. The new bridge will also provide much-needed flood control to secure safe passage for thousands of cars every day — including for emergency vehicles, recreationalists, residents, and commuters — and will provide the public with safe access to beautiful open spaces in the Santa Margarita Trail Preserve, which hosts over 100,000 visitors each year and 18 miles of trails.
After construction began in 2023, the discovery of culturally sensitive items prompted the team to pivot: the bridge alignment was redesigned to run alongside the existing concrete river crossing, honoring the Pechanga Band of Indians’ request not to build over an area of cultural significance to them. The final design is completed, steel girders fabricated, permits revised, and ready to start construction again. Partnerships with Pechanga, NOAA, The Wildlands Conservancy as the landowner, the County of San Diego as the CEQA lead, and state and federal funders have made this unique re-design possible. When finished, the Santa Margarita River will become the first perennial river in Southern California reconnected from the mountains all the way to the ocean for endangered Southern steelhead.
The chokepoint. The existing Sandia Creek Drive crossing, soon to be replaced.
Reduced flood risk. The new bridge will also provide much-needed flood control to secure safe passage for thousands of cars every day
High quality upstream habitat. The Santa Margarita River will become the first perennial river in Southern California reconnected from the mountains all the way to the ocean.
SANTA MARGARITA RIVER, RIVERSIDE & SAN DIEGO COUNTIES
One of the last free-flowing rivers in Southern California.
Real numbers behind the Santa Margarita’s scale, and the bridge replacement project set to reconnect it.
742 sq mi
Basin area — the second-largest river basin in Southern California
29 mi
From headwaters near Temecula to the Pacific Ocean near Oceanside
12+ mi
Of spawning and rearing habitat to be reopened above Sandia Creek Drive
100k+
Annual visitors to the Santa Margarita Trail Preserve’s 18 miles of trails
Part 2 | Pechanga Band of Indians
A Partnership with the Pechanga Band of Indians
The land surrounding the Santa Margarita River holds deep cultural significance for the Pechanga Band of Indians, whose ancestral ties to this watershed run far deeper than the fish passage barrier CalTrout is working to remove. The Santa Margarita River valley is rich in cultural resources from thousands of years of ‘Ataaxum/Payómkawichum People living in and traveling through the valley. Written and oral history communicated through generations of Tribal descendants illuminate areas that have cultural significance, while other areas have sparse visible or historical indicators. The place encompasses a Tribal cultural landscape in which both cultural and natural resources contribute value.
As stewards of this important landscape, the Pechanga care deeply about impacts of projects, and their cumulative impacts, including long-term planning, management, and access. That relationship extends beyond construction logistics for this one project. CalTrout’s Southern California team and Pechanga representative Myra Masiel-Zamora have led walking tours of the Santa Margarita River Preserve, sharing the Tribe’s connection to the land and its responsibilities of stewardship. The result is a restoration project shaped not just by engineering, but by the people whose history is woven into this river.
WATCH · Walking the Preserve with Pechanga
Hear from the people whose history is woven into this river.
CalTrout’s Southern California team and Pechanga representative Myra Masiel-Zamora share the Tribe’s connection to the Santa Margarita River Preserve, and what stewardship of this landscape means to the Pechanga Band of Indians.
Part 3 | Protecting a Rare Undammed River
A River That Escaped Dams
Few rivers in Southern California have escaped the dams, diversions, and channelization that reshaped the region’s waterways over the last century. The Santa Margarita River is one of them — and much of the credit belongs to the land it flows through. Marine Corps Base Camp Pendleton has kept miles of the lower watershed free from development, while The Wildlands Conservancy’s Santa Margarita River Preserve protects thousands of acres of riparian habitat around Sandia Creek and the river’s middle reaches.
That protected, undeveloped character is exactly what makes the final barrier removal so consequential. Unlike many restoration projects that must first undo decades of surrounding urbanization, this one simply has to reopen the last locked door on a river system that has otherwise remained remarkably intact — clearing the way for steelhead to reclaim a nearly complete, high-quality watershed.
0 Dams
on the Santa Margarita River’s mainstem, and One of the last rivers in Southern California that can say that
The Santa Margarita River is one of CalTrout’s clearest opportunities to demonstrate what full watershed reconnection can look like in Southern California. As part of the South Coast Steelhead Coalition, this project stands alongside parallel efforts on the Ventura River, Santa Clara River, and Trabuco Creek — each working toward the same goal of restoring passage for endangered Southern steelhead across the region. Completing the Sandia Creek Fish Passage Project will reopen 12 miles of habitat — and it will prove that a Southern California river can once again run wild from its headwaters to the ocean.
CALTROUT IN ACTION
Stories from the Santa Margarita River.
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New Bridge on Santa Margarita River Will Enhance Important Steelhead Migration Corridor
Read more →: New Bridge on Santa Margarita River Will Enhance Important Steelhead Migration Corridor -
Over $13M Recommended for Funding CalTrout-Led Fish Passage Projects
Read more →: Over $13M Recommended for Funding CalTrout-Led Fish Passage Projects -
Tour the Santa Margarita River with CalTrout and Pechanga Tribe
Read more →: Tour the Santa Margarita River with CalTrout and Pechanga Tribe
Support caltrout
Support projects like the Santa Margarita River
One aging bridge is all that stands between a rare, undammed Southern California river and 12 miles of steelhead habitat waiting to be reopened. Your support helps CalTrout finish the Santa Margarita River Bridge Replacement Project — and reconnect the first Southern California river from the mountains to the ocean.