LOCATION.-- Lat 41°20'17", long 88°51'10" (NAD of 1927), in SW1/4SW1/4 sec.11, T.33 N., R.3 E., LaSalle County, Hydrologic Unit 07130001, downstream of the railroad bridge, 0.25 miles, and downstream 0.5 miles of the Route 23 bridge in Ottawa and the confluence with the Fox River.

DRAINAGE AREA.-- 10,949 mi².

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: March 11, 1903 to December 31, 1903.

PARTIAL RECORD: Miscellaneous discharge measurements, water years 1903-1904.

SURFACE-WATER QUALITY

CHEMICAL: Water years 1997 to 2004.

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

BIOLOGICAL

ALGAE: Water years 1997-99 and 2002-04.

BENTHIC MACROINVERTEBRATES: Water years 1998-99, 2002-04.

FISH: Water years 1998-99, 2002-04.

HABITAT: Water years 1998-2000, 2003.

GAGE.-- Prior to November 1, 1903, vertical staff at west end of first pier from the north abutment of the railroad bridge at same datum. November 1, 1903 to February 21, 1904, chain gage read twice daily. Datum of gage is 579.48 ft above NGVD of 1929 (579.30 ft NAVD 1988).

REMARKS.-- Discharges for surface-water quality data for water years 1997 to current are computed by adding discharges of Illinois River at Marseilles (05543500) and Fox River at Dayton, IL (05552500).

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 46,900 ft³/s, Apr. 15, 1903, gage height, -119.08 ft (460.40 ft above NGVD of 1929); minimum discharge, 6,740 ft³/s, Sept. 8, 1903.

REMARKS FOR CURRENT YEAR.--Benthic macroinvertebrate community samples were collected as part of the National Water-Quality Assessment program (NAWQA) in the lower 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 begins at the red buoy near river mile 239, marking the top of Hitt Island, and continues downstream for 3281 feet, which is 492 feet downstream of the Ottawa navigation light number 238.5. The surface area sampled at reach A was 0.26 m².