LOCATION.-- Lat 41°49'33", long 87°54'02" (NAD of 1927), in NE1/4SE1/4 sec.31, T.39 N., R.12 E., Cook County, Hydrologic Unit 07120004, on left pier at upstream side of bridge on Wolf Road, in Cook County Forest Preserve, 0.5 mi north of Western Springs, and at mile 8.8.

DRAINAGE AREA.-- 115 mi².

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: October 1945 to current year.

STAGE: Water years 1994 to current year.

SURFACE-WATER QUALITY

CHEMICAL: Water years 1978-91 and 1999 to current year.

MISCELLANEOUS: Contaminants in streambed sediments, August 1998; contaminants in fish tissue, August 1998.

BIOLOGICAL

ALGAE: Water years 1989, 1990, and 2002-03.

BENTHIC MACROINVERTEBRATES: Water years 1999 and 2002.

FISH: Water years 1999-2000 and 2002-04.

HABITAT: Water years 1999 and 2002-04.

REVISED RECORDS.-- WSP 1915: Drainage area. WRD IL-87-2: Drainage area. WRD IL-97-2: July 21 - Sept. 26, 1996.

GAGE.-- Water-stage recorder, phone telemeter, and crest-stage gage. Datum of gage is 624.93 ft above NGVD of 1929. Prior to July 26, 1946, nonrecording gage at same site and datum.

REMARKS.-- Occasional regulation by sewage treatment plants upstream from station. Since May 28, 1996, some flow temporarily diverted for flood control to Elmhurst Quarry Flood Control Reservoir 12.3 miles upstream from gage.

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 3,540 ft³/s, Aug. 17, 1987, gage height, 10.54 ft; minimum, no flow, May 27, 1998, due to bridge construction.

REMARKS FOR CURRENT YEAR.--Benthic macroinvertebrate community samples were collected as part of the National Water-Quality Assessment program (NAWQA) in the upper Illinois River Basin. One quantitative (Richest-Targeted Habitat) and one qualitative (Qualitative-Multiple Habitat) sample were collected in accordance with the NAWQA protocols (Moulton and others, 2002). The quantitative sample was a composite of macroinvertebrates from about ten submerged tree branches. Branches were cut underwater, gathered in a 500µm mesh net, and invertebrates were washed or picked from the branches. The average length and average diameter of each branch were measured and used to calculate an approximate surface area. The qualitative sample was collected from many habitat types within the sampling reach to obtain as complete a list of invertebrate taxa as possible. All samples were processed by the USGS National Water-Quality Laboratory. Phylum, Class, Order, Suborder, Family, Subfamily, and Tribe are listed and arranged according to the USGS National Water-Quality Laboratory taxonomic hierarchy. Reach A, lat 41°49'41.60", long 87°54'28.40", is located 187 ft upstream of the walking bridge (0.63 mi upstream from gage) in the Bemis Woods west of Wolf Road and north of Ogden Avenue; it continues upstream for 984 ft. The surface area sampled at reach A was 0.31 m².