LOCATION.-- Lat 41°19'37", long 88°43'03" (NAD of 1927), in SE1/4SW1/4 sec.13, T.33 N., R.4 E., La Salle County, Hydrologic Unit 07120005, on right bank 0.5 mi downstream from Marseilles Dam in Marseilles, 6.9 mi upstream from Fox River, and at mile 246.5.

DRAINAGE AREA.-- 8,259 mi², does not include diversion from Lake Michigan through the Chicago Sanitary and Ship Canal, which has occurred since Jan. 17, 1900.

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: October 1919 to current year. Prior to October 1939, published as "at Morris."

STAGE: Water years 1994 to current year.

PARTIAL RECORD: Annual maximum, water years 1894 to 1919.

SURFACE-WATER QUALITY

CHEMICAL: Water years 1975-97.

SEDIMENT: February 2003 to current year.

SPECIFIC CONDUCTANCE: Water years 1975-81.

WATER TEMPERATURE: Water years 1975-81.

MISCELLANEOUS: Water Year 1998; Contaminants in streambed sediments, October 1996; contaminants in fish tissue, October 1996; sediment concentration and particle size, water years 1993-97, 2003-2005.

BIOLOGICAL

ALGAE: Water years 1989-90, 1996-97.

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

GAGE.-- Water-stage recorder, phone telemeter, automatic water sampler, and U.S. Army Corps of Engineers satellite telemeter. Datum of gage is 452.91 ft above NGVD of 1929 (452.71 ft NAVD 1988). October 1919 to January 1935, nonrecording gage at site at Morris, 16.6 mi upstream, at datum 25.59 ft higher. January 1935 to September 1939, water-stage recorder 300 ft downstream from Morris site at that datum. October 1939 to September 2002, water-stage recorder at current site at datum 10 ft. higher.

REMARKS.-- Figures of daily discharge include flow through navigation locks. Flow regulated by powerplants and navigation dam above station. Since Jan. 17, 1900, flow has included diversion from Lake Michigan through Chicago Sanitary and Ship Canal. Suspended sediment samples were collected twice weekly with additionl samples during high-runoff periods by an automatic water sampler.

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 95,000 ft³/s, Feb. 22, 1997, gage height, 26.85 ft, present datum; minimum daily discharge, 461 ft³/s, Nov. 21, 2002.

SUSPENDED-SEDIMENT CONCENTRATIONS: Maximum daily, 307 mg/L, June 13, 2004; minimum daily, 6 mg/L, Jan. 28 - Feb. 6, 2004.

SUSPENDED-SEDIMENT LOADS: Maximum daily, 43,400 tons, Jan. 14, 2005; minimum daily, 37 tons, Feb. 4, 2004.

EXTREMES OUTSIDE PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Flood of May 6, 1892 reached an estimated discharge of 72,500 ft³/s, stage not determined. A stage of 26.2 ft at Morris occurred in 1831, discharge not determined, and a stage of 35.4 ft (ice jam) occurred at present site and datum on Jan. 21, 1916, estimated discharge, 40,000 ft³/s.