Water Quality Improvement Project
Issaquah Creek Basin:
The Issaquah Creek Basin is located on Washington State’s I-90 corridor at
the south end of Lake Sammamish in western King County. The basin consists of
the stream networks and watersheds of Issaquah and Tibbetts creeks, and
contains most of the city of Issaquah. Streams in the Issaquah Creek Basin
provide important resources for fish, primary contact recreation, education, and
Water quality issues
Issaquah Creek Basin streams have too much bacteria, as measured by fecal
coliform bacteria counts in the water. Because of this, these streams were
placed on the state's 303(d) list of impaired waters for 1998. The federal Clean
Water Act requires that streams on a state's 303(d) list have a total maximum daily
load (TMDL) or other appropriate water cleanup plan developed. The TMDL
or other appropriate water cleanup plan must determine the extent of the
impairment, how much pollutant the water body can actually accept without
violating the state's surface water quality standards (loading capacity),
and how much the pollutant load must be reduced so that the water body meets the
water quality standard for that pollutant (wasteload or load allocation).
Sources of bacteria contamination in the Issaquah Creek Basin include on-site
septic systems; possible sanitary sewer line leaks; agriculture (commercial and
small farms); landfills; and wildlife. Urban stormwater and stormwater runoff
from roads and highways also carry bacteria to the streams.
Water intake facility that provides water for the Issaquah Creek Salmon Hatchery and a series of boulder weirs built in 2012. This replaced an outmoded dam and fish ladder built in 1937. © Larry Franks, FISH Member.
Why this matters
Fecal coliform is a type of “bacteria” common in human and animal waste. It
indicates that sewage or manure is entering a water body. As the level of fecal
coliform increases, the risk of people getting sick from playing or working in
the water increases. Bacteria can get into our waters from untreated or
partially treated discharges from wastewater treatment plants, from improperly
functioning septic systems, stormwater drainage systems, and from livestock, pets and wildlife.
People can help keep bacteria out of the water. Properly collect, bag, and
trash dog poop. Check your on-site sewage system to make sure it is maintained
and working properly. Ensure livestock and manure are kept away from the water.
Status of the project
Washington State Department of Ecology (Ecology), along with local
governments, citizens, and special interest groups, developed a water quality
improvement report (also called a TMDL). This TMDL included a water
cleanup plan that detailed suggested methods and initial efforts to reduce fecal
coliform bacteria loading to the Issaquah Creek Basin. After addressing comments
from public review, Ecology submitted the TMDL to EPA. EPA approved the
TMDL in October 2004.
Issaquah Creek Basin Water Cleanup Plan for Fecal Coliform Bacteria: Submittal Report
Focus on Bacteria in the Issaquah Creek Basin (Ecology publication)
City of Issaquah - Rainier Boulevard Street LID Improvement Project
WRIA 8: Cedar-Sammamish-Lake Washington Watershed Information (Environmental Assessment
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