Final Mitigated Negative Declaration and Response to Comments

IX.
HYDROLOGY AND WATER QUALITY.
ENVIRONMENTAL SETTING
The climate of the Lake Tahoe region is generally Mediterranean, but is modified by
topography and geography. It is characterized by relatively warm, dry summers interrupted by
occasional lightning storms, and cold wet winters with variable precipitation mostly falling as
snow. About 95% of the precipitation falls between October and May. An average of more
than 80 inches of precipitation falls on the west side of the Lake Tahoe Basin, mostly as snow
(Boughton et al. 1997). The annual mean temperature is 45 degrees. The coldest month is
February, with an average temperature of 28 degrees. Average summer temperatures range
from 60 to 80 degrees during the day, and from 35 to 40 degrees at night. Snow accounts for
75% to 80% of the total precipitation, with an average snowfall of 200 to 325 inches. The
normal average precipitation in the basin is 34 inches.
Infrequent large, warm winter storms can potentially produce extreme streamflows and flooding
resulting from high rainfall and melting of existing snowpack. The seasonal snowmelt process
results in peak streamflows between May and June. Minimum streamflows occur during late
summer and fall.
Lake Tahoe is recognized as an Outstanding National Resource Water by the U.S.
Environmental Protection Agency’s Water Quality Standards Program and the Clean Water
Act. Under this designation, Lake Tahoe is afforded the highest protection from degradation
(TRPA 2002). The Water Quality Control Plan for the Lahontan Region (LRWQCB 1994
Chapter 5: Water Quality Standards and Control Measures for the Lake Tahoe Basin) has
designated beneficial uses for the surface waters of the Lake Tahoe Hydrologic Unit, such as
Cold Freshwater Habitat. The Cold Freshwater Habitat (COLD) definition is “beneficial uses of
waters that support cold water ecosystems including, but not limited to, preservation and
enhancement of aquatic habitats, vegetation, fish, and wildlife…” For all waters designated
COLD, the temperature shall not be altered. Other Beneficial Uses such as municipal water
supply and recreational uses are discussed under other sections of this document.
Lake Tahoe is considered to be an oligotrophic lake, with low concentrations of nutrients, low
algal productivity, and high oxygen content. These factors lead to its exceptional clarity. There
has been a significant decline in water clarity since 1968 (UC Davis 2010). Current concerns
are attributed in part to the increased algal growth caused by nutrient inputs from development
of the Lake Tahoe watershed. Control of nutrient inputs to the lake has thus become one of
the priorities of regulatory agency action in the basin.
Asian Clam Control Project IS/MND
Emerald Bay State Park
California Department of Parks and Recreation
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