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King County Water Quality Monitoring

King County monitors the ecological health of Idylwood Creek in a variety of ways including collecting and analyzing water, sediment, and benthic invertebrate samples. Water quality samples have been collected monthly at Station A620 located at the footbridge in Idylwood Park. Sampling at this site began in 1995 and continued until 2008 when budget cutbacks forced King County to reduce the breadth of its water quality monitoring program. Sampling at this site resumed in February 2013. Sediment samples have been collected from Idylwood Creek as part of the Streams Sediment Monitoring Program starting in 1987. King County began collecting benthic macroinvertebrate samples in Idylwood Creek in 2002.

From time to time special studies have been conducted at various streams in King County. Click here for information about Special Studies of Idylwood Creek.

Watershed

Water Shed Image The Idylwood Creek watershed is located at the northwest end of Lake Sammamish in the City of Redmond. Headwaters of the creek originate in the City of Bellevue. The creek drains into Lake Sammamish roughly 50 feet north of the swimming beach area in Idylwood Park.

Fisheries

Volunteers with the Salmon Watcher Program have been making observations at various locations within the Idylwood Creek basin since 2000. No fish were observed in Idylwood Creek during the 2004 observation period (King County WLRD April 2005).

Water Quality

Water quality samples are analyzed monthly for temperature, dissolved oxygen (DO), pH, conductivity, turbidity, total suspended solids, ortho-phosphorus, total phosphorus, ammonia, nitrate-nitrogen, total nitrogen, and fecal coliform bacteria (FC). Results are compared to State water quality standards. Water quality standards are designed to protect public health and aquatic life. Comparing monitoring results to water quality standards allows an understanding of how safe the creek is for recreational contact as well as for aquatic life. (See link at top of page to view current water data.)

State water quality standards were revised in 2003. Idylwood Creek is now categorized as “Core Summer Salmonid Habitat” for aquatic life use, and “Extraordinary Contact” for recreational use. The creek is on the 2012 Washington Department of Ecology's (Ecology) 303(d) list for violation of dissolved oxygen and fecal coliform bacteria standards (Category 5). See Table 1 for a summary of water quality violations in the creek during the most recent water year.

To view charts of current water quality conditions in the creek, please visit the links at the top of the page.

Water Quality Index

A Water Quality Index (WQI) rating system was developed by the State Department of Ecology that evaluates several water quality parameters and gives a single rating of “high,” “moderate,” or “low” water quality concern. To see how Idylwood Creek ratings compare with other stream sites, visit the Water Quality Index page.

Table 1. Routine monitoring summary statistics for this station from 1995 to 2017
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)20110.77.912.810.51.1
Temperature (°C)32112.11.720.113.03.6
Turbidity (NTU)2225.750.50460.001.3435.74
pH2207.706.608.507.720.28
Conductivity (mSIEMS/cm)179221.045.0340.0237.055.2
Total Suspended Solids (mg/L)22214.650.501180.001.30103.86
Ortho-Phosphorus (mg/L)2220.02120.00750.09900.02020.0104
Total Phosphorus (mg/L)2220.04240.01490.63100.03240.0558
Ammonia (mg/L)2220.02450.00530.38800.01880.0319
Nitrate (mg/L)2220.54860.22401.32000.50800.1973
Total Nitrogen (mg/L)2220.75360.34402.89000.63900.3540
Fecal Coliform(CFU/100ML)3204984180002001528

Table 2. Storm water monitoring summary statistics for this station from 1995 to 2017
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)4810.48.712.310.31.1
Temperature (°C)5711.45.916.711.12.9
Turbidity (NTU)5825.041.50434.007.3175.75
pH557.486.807.897.500.25
Conductivity (mSIEMS/cm)44118.347.0174.0124.034.5
Total Suspended Solids (mg/L)5847.950.70769.0010.05136.65
Ortho-Phosphorus (mg/L)580.03350.00650.16600.02800.0239
Total Phosphorus (mg/L)580.10040.03230.73500.05560.1221
Ammonia (mg/L)580.02560.01100.08320.02050.0139
Nitrate (mg/L)580.57340.21901.80000.47900.3003
Total Nitrogen (mg/L)580.95000.59302.26000.83150.3518
Fecal Coliform(CFU/100ML)58162180140009052264

Hydrology

King County is not currently operating any stream, rain, or temperature gages in Idylwood Creek.

Stream Sediment

Sediment data were collected from Idylwood Creek as part of the Stream Monitoring Program starting in 1987. Data were compiled and analyzed for the years 1987 through 2002. Data were analyzed for trends, correlations, and were compared to sediment quality guidelines. No significant trends were identified during data analysis for any of the parameters tested. Results indicate that Idylwood Creek sediments exceeded on sediment quality guideline (nickel). Of the 27 streams monitored in King County, Idylwood Creek had the 7th lowest metals concentrations.

Benthic Invertebrates

Benthic macroinvertebrates are small animals visible to the naked eye (macro) that lack a backbone (invertebrate) and live in or around the streambed (benthic). This group includes aquatic insects (such as mayflies and dragonflies), crustaceans, clams, snails, and worms. Benthic macroinvertebrates are of interest to scientists and water resource managers because they are an excellent indicator of the biological health of stream ecosystems and are a critical component of the food web in aquatic communities. Scientists quantify the composition and diversity of benthic macroinvertebrate populations in a stream to compare the biologic integrity of different streams. King County has utilized benthic macroinvertebrate sampling to assess biological health of numerous creeks across the county (see map).

For more information about benthic macroinvertebrates and King County’s Benthic Macroinvertebrate Program, please visit the King County Stream Bug Monitoring web page. To see the benthic macroinvertebrate data for Idylwood Creek, please visit the Puget Sound Benthos webpage.

Special Studies

Water Resources Inventory Area (WRIA) 8

In WRIA 8, citizens, scientists, businesses, environmentalists and governments are cooperating on protection and restoration projects and have developed a science-based plan to conserve salmon for future generations. Visit the WRIA 8 page to see how Idylwood Creek is part of this WRIA 8 planning process.