Local community helps make Dalton Lake restoration project a reality

Construction crews recently completed work reconnecting a historic floodplain lake to the Lower Columbia River Estuary, improving salmon access to backwater habitat for rearing juveniles during outmigration.

Located along the Columbia River Highway, just north of St. Helens, Oregon, is Dalton Lake, site of the Dalton Lake restoration project. It is the only undeveloped tidal wetland habitat within five miles in either direction along the Columbia River that contains over 150 species of birds and waterfowl, beavers, otters, reptiles and amphibians.

Sponsored by the Columbia River Estuary Study Taskforce (CREST) with funding from BPA’s Fish & Wildlife Estuary Program, this estuary restoration project reconnects tidal flows and provides fish access between Dalton Lake and the Columbia River to areas that were cut off by an earthen berm and water control structure built in the 1990s.

This effort represents the coming together of multiple local groups in the St. Helens area to enhance this highly valued natural habitat. The land is managed by the St. Helens Parks and Trails Commission, the City of St. Helens, Oregon Department of Transportation, Columbia Drainage Vector Control and the Dalton Lake Nature Preserve Advisory Committee (or Friends of Dalton Lake), a group created by local citizens to preserve the unique ecosystem attributes of the area.

“The Dalton Lake project, being adjacent to the mainstem Columbia River, is ideal for juvenile fish to rest and feed as they make their way out to the ocean,” said BPA Fish and Wildlife project manager Anne Creason. “In addition, the project’s location along the estuary is in an area that will especially benefit from juvenile salmon habitat improvements. The project is also a great example of how a true community effort can result in an implementable project.”

Dalton Lake impacted by highway expansion

In the early 1990s, ODOT widened a nearby section of the Columbia River Highway, which impacted an adjacent wetland, requiring wetland mitigation. Dalton Lake was selected as the mitigation site, and a restoration plan was drawn up. A central goal of the plan was to stop the spread of reed canary grass, an invasive plant that was the primary threat to the health of the wetlands. This plant is known for choking out native plant species and impacting wetlands by altering hydrology. Restoration at that time included construction of an earthen berm across the outlet of the lake.
“Now, at that time, the key priority for ODOT was actually controlling invasive vegetation species,” explained Tracy Hruska, a habitation restoration project manager at CREST. “And the thinking in that era was that reed canary grass, which was a target invasive species, could be controlled by inundation. The easiest way to control inundation is by building a water control structure.”
In theory, the water control structure would hold more water in the lake, flooding out the invasive reed canary grass. 

In practice, the structure was not effective. The reason? Resident beavers built a dam upstream from ODOT’s water control structure, which held more water in the lake than the artificial version did. The water control structure did little more than create an additional barrier to fish trying to reach the lake and limited tidal flows from the river up into the lower section of the outlet channel. Many water control structures like this one were installed around the greater Portland area in the 1990s on the theory that they were a durable engineering solution to an ecological problem. Most of those structures are now being removed, as restoration practitioners learn that they often do more harm than good.

“They (juvenile salmon) have a limited amount of time as they move downstream to gain body mass and undergo their own physiological adaptation to salt water. So places like Dalton Lake are really key for ensuring that juvenile salmon have reached the growth stage and are at the fittest level possible before they get to the ocean just beyond Astoria,” said Hruska.

Restoring the lake

For years, local discussions took place on ways to fix the problem, but solutions were expensive and the large number of local stakeholders in the community created additional complexity. Issues such as what to do about the beaver dams were slowly worked through. In 2020, CREST approached ODOT about restoring the site to address the artificial berm barrier and the ineffective water control structure. 

With ODOT, and later, the city of St. Helens on board, CREST went to BPA Fish & Wildlife for project funding. BPA, together with the U.S. Army Corps of Engineers, manages several of the hydroelectric dams on the Columbia River and is legally responsible for mitigating the impact that the dams have on federally protected salmon. In the Columbia River Estuary, the focus is on restoring tidal wetlands like Dalton Lake to increase foraging and rearing opportunities for outmigrating juvenile salmon. Dalton Lake, with its 34 acres of wetland habitat, was an obvious candidate for restoration. 

The BPA-funded restoration project was completed this fall. The berm and water control structure have been removed. Visitors to the lake will now find a new 65-foot bridge that replaces the trail access previously provided by the berm. Log structures have been added to the outlet channel to slow water velocities, provide cover, and force the channel to develop a bumpy bottom like a natural channel, all of which encourages use by juvenile salmon. In addition, these logs provide beavers anchoring points for additional dams, increasing the likelihood the beavers remain in the area and maintain lake water levels. Upstream of the log structures, CREST removed reed canary grass and lowered elevations to prevent regrowth of this invasive species.   

While the bridge and trail are now open to the public for recreational use, visitors will have to wait a little longer to see the native vegetation grow back. Crews will return to the site in the winter to install thousands of wetland and forest plants to cover the areas disturbed by construction. CREST will monitor the site for the next five years to make sure the restored habitat is functioning as intended
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Read more about Dalton Lake.