LOCATION.-- Lat 40°37'48", long 87°43'26" (NAD of 1927), in NW1/4NE1/4 sec.16, T.25 N., R.12 W., Iroquois County, Hydrologic Unit 07120002, on pier at downstream side of bridge on County Highway 9,200 ft downstream from Mud Creek, 1 mi west of Milford, and at mile 23.9.

DRAINAGE AREA.-- 446 mi².

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: July 1948 to current year.

STAGE: Water years 1994 to current year.

SURFACE-WATER QUALITY

CHEMICAL: Water years 1978-91, and 1999 to 2004.

MISCELLANEOUS: Water years 2004 and 2005; Contaminants in streambed sediments, August 1999; contaminants in fish tissue, August 1999.

BIOLOGICAL

ALGAE: Water years 1999, 2002-04.

BENTHIC MACROINVERTEBRATES: Water years 1999, 2002-04.

FISH: Water years 1999, 2002-04.

HABITAT: Water years 1999-2000, 2002-04.

REVISED RECORDS.-- WDR IL-75-1: Drainage area.

GAGE.-- Water-stage recorder and phone telemeter. Datum of gage is 622.00 ft above NGVD of 1929 (621.80 ft NAVD 1988). Prior to July 23, 1970, nonrecording gage at same site and datum.

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 22,900 ft³/s, Feb. 21, 1951, gage height, 20.90 ft, from rating curve extended above 8,200 ft³/s; maximum gage height, 28.16 ft, Apr. 12, 1994, discharge, 19,400 ft³/s; minimum discharge, 2.0 ft³/s, Sept. 1, 2, 7, 1972, Oct. 8, 1994.

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 is located 512 ft downstream of the the 1100 N Road bridge (which is 2.5 stream miles downstream of the gage), and continues downstream for 820 ft which includes the area next to the gaging station. The surface area sampled at reach A was 0.27 m².