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NONPOINT SOURCE SUCCESS STURY

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Lake Tahoe Investments Yield a Decade of Progress

Waterbody Improved

Lake Tahoe's clarity declined by one-third between the 1960s
and 2000, threatening the lake's value as an international tourist
destination and drinking water source. The roadmap for reducing pollutant loads to the lake,
called the Lake Tahoe Total Maximum Daily Load (TMDL) Implementation Plan, was collaboratively
developed and adopted by the California Lahontan Water Board (LWB) and the Nevada Division of
Environmental Protection (NDEP). The TMDL is currently being implemented by public and private
partners. A 2021 performance review indicated implementation progress has successfully achieved
10-year pollutant load reduction targets. As a result, water clarity has stabilized.

Problem

Nestled in the Sierra Nevada Mountains on the border
of California and Nevada, Lake Tahoe's uncommonly
clean water allows sunlight to reach much greater
depths than most other water bodies (Figure 1). Due to
Lake Tahoe's remarkable clarity, averaging over 97 feet
annually before the 1960s, Nevada designated the lake
a Water of Extraordinary Ecological or Aesthetic Value.
However, one-third of Lake Tahoe's clarity was lost by
the year 2000, and a TMDL was initiated.

To address clarity in Lake Tahoe, the LWB and NDEP
collaborated to develop the watershedwide Lake
Tahoe TMDL to attain the numeric target of 97.4 feet
of annual average clarity. After a decade of develop-
ment using new and best available science, the TMDL
was adopted by California and Nevada and approved
by the U.S. Environmental Protection Agency in 2011.

TMDL research found Lake Tahoe's clarity decline is
due to increased fine sediment particles (FSP) and
algae fed by nitrogen (N) and phosphorus (P). The
TMDL found the largest source of FSP to be urban
stormwater loads, forested upland runoff, stream
channel erosion, and atmospheric loading. FSP and
algae affect clarity by reducing the amount of light
that can penetrate the water column. The TMDL lays
out a roadmap to restore historic clarity to 97.4 feet by
2076, which requires FSP, N, and P loads to be reduced
by 65%, 10%, and 35%, respectively. Approximately
half of these reductions are needed to meet the
interim Clarity Challenge milestone of 78 feet of clarity
by 2031 (Figure 2).

Figure 1. Lake Tahoe is on the Nevada-California border.

Story Highlights

Because clarity is slightly more responsive to FSP than
nutrients, current implementation is focused on FSP
reduction. Reducing forest, stream, and atmospheric
FSP loads is important to achieving goals, but because
urban stormwater makes up over 70% of FSP loading,
attaining clarity hinges on reducing urban stormwater
loads (Figure 3).

Douglas and Washoe counties in Nevada collaborate
with the Nevada Department of Transportation to
implement the TMDL through interlocal agreements
established with NDEP, in lieu of municipal separate
storm sewer system permits. These TMDL partners
implement the following pollutant controls to reduce
loads entering Lake Tahoe: (1) ensuring roadway

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operations use advanced practices and best available
technology (BAT) equipment to target application and
improve recovery of wintertime traction abrasives;
(2) constructing stormwater treatment facilities and
infrastructure improvements to capture and infiltrate
stormwater runoff; (3) implementing erosion control
measures to reduce pollutant sources; and, (4) in the
counties, installing parcel-scale-based best manage-
ment practices (BMPs) that capture and infiltrate run-
off on-site. Nevada will continue to implement these
pollutant controls to meet pollutant load reduction
targets specified in interlocal agreements that ramp up
over time.

Results

A performance review conducted in 2021, the 10-year
anniversary for TMDL implementation, indicated
Nevada urban implementers had reduced average
loads for FSP by 150,000 pounds per year (Ibs/yr)
and P and N loads by over 460 Ibs/yr and 1,400 lbs/
yr, respectively. These reductions exceeded 10-year
targets. Actions to reduce pollutants entering the lake
through forestland runoff, erosion of stream beds and
banks, and air deposition were also on track to achieve
10-year goals. The overall conclusion was that 10-year
pollutant load reduction milestones were achieved.
Due to progress in achieving load reductions, clarity
levels have stabilized over the last 20 years.

However, climate change is challenging the progress
toward achieving TMDL goals by leading to more
extreme precipitation events; an increased threat of
wildfire from extended drought; increased stream
temperatures that can affect pollutant load insertion
depth; and alterations to internal lake dynamics, such
increased duration of stratification and the suppres-
sion of mixing and upwelling events that help flush
out the water column. The Lake Tahoe TMDL Program
remains committed to collaborating with the Lake
Tahoe Science Advisory Council to better understand
processes, drivers, and impacts The partners continue
to implement effective pollution controls and adap-
tively manage the program in response to research
findings and recommendations.

Partners and Funding

Over $1 billion has been spent watershedwide by local,
state, and federal natural resource management agen-
cies and the private sector to improve water quality.
Within Nevada, the Nevada Division of State Land's

The Clarity Challenge

1963	1968	2008	2028	2076

YEAR

Figure 2. I he Clarity Challenge Milestone infographic.

Fine Sediment Particle Load Reductions

Figure 3. Urban lands contribute most pollutant load.

Water Quality and Erosion Control Grant Program
and Lake Tahoe Restoration Act Erosion Control Grant
Program administered by the U.S. Forest Service
has funded stormwater treatment/erosion control
projects. The Nevada Nonpoint Source (NPS) Pollution
Management Program has provided over $1 million in
Clean Water Act (CWA) section 319(h) funds for these
project types since 2000. Additionally, the Nevada NPS
program has provided Washoe and Douglas coun-
ties almost $850,000 in CWA section 319(h) funds to
purchase BAT equipment for advanced road opera-
tions, and over $3.25 million to facilitate installation of
parcel-level BMPs over the same timeframe.

Additionally, the Nevada NPS program has provided
almost $350,000 to several stream restoration proj-
ects. While fish passage improvement was the primary
objective, the multibenefit component featured water
quality improvement by enhancing riparian vegetation
and stabilizing channels. Nearly $450,000 was pro-
vided to support TMDL research and planning activi-
ties, and roughly the same amount was provided for
education and outreach efforts in the watershed.

^£D	U.S. Environmental Protection Agency

0** Office of Water
\ Washington, DC

I

EPA 841-F-23-001H
pRot^° September 2023

For additional information contact:

Jason Kuchnicki

Nevada Department of Conservation and Natural
Resources, Division of Environmental Protection,
Bureau of Water Quality Planning
775-687-9450 • kuchnicki@ndep.nv.gov

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