LOCATION.-- Lat 40°17'39", long 90°04'06" (NAD of 1983), in NE1/4SW1/4 sec.1, T.21 N., R.9 W., Mason County, Hydrologic Unit 07130003, on left bank 100 ft downstream from U.S. Highway 136 bridge, 0.8 mi downstream from mouth of Spoon River, and at mile 119.6.

DRAINAGE AREA.-- 18,299 mi².

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: October 1921 to September 1927, June 1985 to September 1989. January 1907 to March 1917, from Flood-Control Report, Illinois Division of Waterways, 1929; April 1917 to September 1921, October 1928 to September 1961, from report of the National Weather Service; October 1961 to September 1967, in files of U.S. Army Corps of Engineers.

STAGE: Gage-height records collected at site October 1878 to May 1881, January 1896 to December 1904 are contained in House Document 263, 59th Congress, 1st Session, Des Plaines and Illinois Rivers.

SURFACE-WATER QUALITY

MISCELLANEOUS: Contaminants in streambed sediments, October 1996; contaminants in fish tissue, October 1996.

GAGE.-- Water-stage recorder and point-velocity meter. Datum of gage is 424.40 ft above NGVD of 1929 (levels by Army Corps of Engineers) (424.08 ft NAVD 1988). October 1921 to September 1927, nonrecording gage at same site at datum 424.76 ft above mean sea level, adjustment of 1912.

REMARKS.-- Occasional regulation at low flow by navigation dams at Peoria and La Grange. Since Jan. 17, 1900, flow has included diversion from Lake Michigan through Chicago Sanitary and Ship Canal.

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 74,600 ft³/s, Oct. 12, 1926, gage height, 23.4 ft; minimum daily discharge, 4,100 ft³/s, Sept. 10, 1988.

EXTREMES OUTSIDE PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 90,300 ft³/s, Mar. 9, 1985 (by discharge measurement), gage height, 26.30 ft; maximum gage height, 27.3 ft, May 25, 1943.