Tahoe’s natural filters: Preserving, restoring wetlands essential to lake clarity

Claire McArthur
Tahoe Daily Tribune
The Upper Truckee Marsh restoration project will revive 250 acres of Lake Tahoe’s largest wetlands. (Photo provided by California Tahoe Conservancy)

Every spring, the snow begins to melt and make its way down the mountains, across marshes and meadows, and through the 63 tributaries flowing into Lake Tahoe.

The water flowing down Tahoe’s 501-square-foot watershed — of which the lake itself takes up about 38% — helps raise the fluctuating lake level. But the route that the water takes before eventually ending up in the lake is crucial to maintaining Tahoe’s famed clarity.

Why, you might ask? It’s all about those SEZs. Stream environment zones are a Tahoe-specific term, meaning “an area that owes its biological and physical characteristics to the presence of surface or groundwater,” according to the Tahoe Regional Planning Agency. Meadows, marshes, streams, streambanks, and beaches are all examples of SEZs that play a critical role in water quality by acting as Tahoe’s natural filtration system, sifting out nutrients and fine sediment, and attenuating floods during high flows.

“There are several different mechanisms for how the wetlands can pull the pollutants out of the water,” explains Stuart Roll, senior environmental scientist with the California Tahoe Conservancy. “One is nutrient uptake by plants absorbing the nutrients in the water, but also water filters down into the wetlands through infiltration. One of the most interesting ways is through a sticky substance on the vegetation called biofilm. As sediment-laden water filters through, the vegetation is sticky enough to pull out those really fine particles before they flow into the lake.”

In the Tahoe Basin, there are approximately 21,944 acres of SEZ, constituting roughly 11% of the land area. But due to a lack of understanding of the wetlands, early development destroyed much of these important pieces of land.


The 1950s, post-World War II boom brought more tourists to Tahoe in cars. The more people that visited, the more development was needed to meet the demand, culminating in the 1960 Winter Olympics in Squaw Valley, which put Tahoe on the international map.

“From there, that’s really when development started heading for the most beautiful parts of Lake Tahoe,” says Jeff Cowen, public information officer for the TRPA. “There was so much private land, and everywhere that people wanted to develop had a good scenic view so it was the lakeshore and meadows. Meadows are beautiful to look at, and you don’t have to do a lot of grading or tree cutting.”

Streambeds and riverbeds were straightened and lowered so they wouldn’t follow their natural path or flood, and meadows, marshes and wetlands were filled to make buildable land. Pollution from the roadways and wastewater flowed into the lake.

After two decades of rapid growth, conservationists had had enough. Scientists began to notice the impact on lake clarity, including environmental pioneers like Dr. Charles Goldman who made the connection between ammonia-rich wastewater dumped into Tahoe and increased algal growth.

“Dr. Goldman sounded the alarm bell that if these kinds of practices continued, that we would lose Lake Tahoe,” Cowen said. “It would go from an oligotrophic lake, clear and low in nutrients, to a eutrophic lake, green with algae and a ton of nutrients. That isn’t what Tahoe was — what made it so special.”


In 1969, in an effort to unite the numerous jurisdictions around the lake and curb unchecked development, the Bi-State Compact was adopted by California and Nevada, and the TRPA was formed. In 1982, the compact was revised to adopt and enforce environmental quality standards, including for Tahoe’s natural filters.

By this point, 4,400 acres of SEZs in the basin were classified as “disturbed, developed or subdivided.” The goal has been to restore 25% of these wetlands to attain a 5% total increase in the area of naturally functioning wetlands. To date, 1,057 acres have been restored across the basin thanks to multi-agency efforts.

This summer marks the second year of work on the largest wetland project to date — the restoration of the Upper Truckee Marsh. In the 50s and 60s, construction of the Tahoe Keys neighborhood in South Lake Tahoe destroyed much of the 1,600-acre marsh. Wetlands were dredged and filled, and the Upper Truckee River was channelized as it nears the lake.

Spearheaded by the Tahoe Conservancy, the agency and its partners are reviving 250 acres of floodplain by restoring the flow of the Upper Truckee River into the middle of the marsh in a series of historic channels and creating 12 acres of wetlands near the Tahoe Keys Marina destroyed by development. Improvements will also be made to the trail to Cove East Beach. The project is set to be completed in 2023.

“Certainly from a water-quality angle, about a third of the land area in the Tahoe Basin drains through the marsh, which is a huge amount of watershed area,” says Roll. “It’s one of the best water filters we have and will certainly help lake clarity.”


New research shows that restoration of Tahoe’s wetlands has impacts beyond lake clarity.

“What we’re seeing more and more is how important these areas are under a changing climate,” says Roll.

Not only do restored marshes stay wetter during extended droughts, providing essential wildlife habitat, but they also capture and store atmospheric carbon dioxide.

“Impaired wetlands can actually be a carbon source, while functional wetlands can be a carbon sink and have comparable carbon sequestration benefits to the rainforest,” notes Roll.

With a grant from the California Department of Fish and Wildlife, the Conservancy is measuring carbon sequestration in the Upper Truckee Marsh before and after its restoration.

While it’s certainly exciting to be a part of the largest wetlands restoration project in the Tahoe Basin, Roll points out that it’s important to remember that it’s one of hundreds of lake-saving projects — from wildfire fuels reduction to greener transportation — identified by state, federal and local agencies in the TRPA’s Environmental Improvement Program.

“At lot of times we get focused on the river itself or the project itself and forget about the larger context,” he adds. “We’re really trying to think beyond the river channel and explore how the projects connect with each other through landscaping, forestry, stormwater projects and aquatic invasive species. We need to think of these all collectively and remember the larger watershed context.”

Editor’s note: This story appears in the 2021 summer edition of Tahoe Magazine.

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