Everything Lake Tahoe lovers should know about Stream Environment Zones | TahoeDailyTribune.com

Everything Lake Tahoe lovers should know about Stream Environment Zones

Claire Cudahy
The California Tahoe Conservancy's restoration of 500-acres of the Upper Truckee Marsh will be the largest SEZ project to date.
Courtesy / California Tahoe Conservancy |

Balancing environmental preservation and infrastructure development in Lake Tahoe is no simple task — and it’s one that is often misunderstood by those outside of the agencies responsible for maintaining that balance.

With large projects in the works on the South Shore like the redevelopment of the Knights Inn property — which includes the construction of a new shopping center plus the partial restoration of an important watershed — readers are encountering Tahoe-specific jargon that may leave them scratching their heads. For instance, what exactly is a Stream Environment Zone? And, more importantly, why does it matter?

A Stream Environment Zone (SEZ) is a term unique to the Lake Tahoe Basin used by the Tahoe Regional Planning Agency (TRPA) to describe “an area that owes its biological and physical characteristics to the presence of surface or ground water.”

“Meadows, marshes, streams, areas adjacent to streams, springs and other low-lying areas that don’t drain well and tend to be wetter and have vegetation that is characteristic of wet areas,” said Stuart Roll, program supervisor in the resources and public access program at California Tahoe Conservancy, one of the agencies responsible for monitoring and restoring SEZs.

A Stream Environment Zone (SEZ) is a term unique to the Lake Tahoe Basin used by the Tahoe Regional Planning Agency (TRPA) to describe “an area that owes its biological and physical characteristics to the presence of surface or ground water.”

These wetland areas act as Lake Tahoe’s natural water filters, capturing sediments and nutrients before the water flows into the lake.

“We have very flashy stream systems here. Sometimes they have a little bit of water in them and other times much greater flows of water. Especially in these high flow periods, like the winter we’re experiencing right now, as you look around the basin you can see we’re having flooding in all sorts of areas,” explained Dan Segan, TRPA principal natural resource analyst.

“And the SEZs, as the water floods, the sediments and nutrients, the primary pollutants that cause a loss of clarity in the lake, get deposited on the flood plane and then are really processed there. So they are entrained there and don’t actually end up in the lake where they are impairing water quality.”

There are 63 streams that flow into Lake Tahoe and approximately 21,944 acres of SEZ, constituting roughly 11 percent of the Basin.


Prior to the 1982 adoption of the TRPA’s environmental quality standards, called thresholds, 4,400 acres of SEZs were classified as “disturbed, developed or subdivided.”

The goal has been to restore 25 percent of these SEZ lands to attain a 5 percent total increase in the area of naturally functioning SEZ lands.

To date, 924 acres of SEZ has been restored — just shy of the 1,100-acre goal. (Historically, the TRPA has not included restoration projects completed by the USFS in the 1980s, which included 680 acres, in this number.)

“A lot of the impairment of SEZs in the basin is when we’ve channelized river systems and prevented water from going down its natural path,” said Segan. “Another part of that is preventing the river from flowing out of its natural boundaries and creating wetlands that are the SEZ itself.”

The most notable example of an SEZ disturbance was the development of the Tahoe Keys in the 1950s and 60s on a large portion of Lake Tahoe’s biggest SEZ, the Upper Truckee Marsh.

“About half of the marsh area was developed so the valuable marsh habitat was lost to that, but also the river itself was channelized into a straight ditch that runs through the marsh and goes directly into the lake,” explained Roll. “The river carries most of the sediment through the marsh and out into the lake instead of spreading out over the marsh like it once did prior to development.”

The California Tahoe Conservancy is in the planning and engineering phase of the project to restore the remaining 500 acres of the marsh to its original state. This will be the largest SEZ restoration project ever attempted. Construction is expected to start in 2019 or 2020 and will take four years to complete.

The Knights Inn project, spearheaded by the city of South Lake Tahoe, will also restore a portion of the 850-acre Bijou Park Creek watershed in its first phase of construction. City officials hope to secure more funding to do further work on the remainder of the watershed, which extends from Heavenly Mountain Resort down to the shoreline. Demolition of the Knights Inn is anticipated to start in June or July.


These SEZ restoration projects can only mean good things for the health of Lake Tahoe.

The average annual clarity for Lake Tahoe in 2015, released in April 2016, was 73.1 feet — a 4.8-foot decrease from the previous year. The decline was due in part to warmer inflowing water caused by a low snow-to-rain ratio. Clarity for 2016 has not yet been released, but will likely be affected by above average precipitation.

But SEZs are important to the Lake Tahoe region beyond their water quality benefits.

“The plant associations of SEZs constitute only a small portion of the basin’s total land area … [but] are perhaps the single most valuable plant communities in terms of their role in providing for wildlife habitat, purification of water, and scenic enjoyment,” according to 1986 TRPA document.

As the communities surrounding Lake Tahoe work to strike a balance between economy and environment, the restoration of SEZs will continue to be a vital part of maintaining and improving the region’s environment.

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