USGS Water-Year Summary 2024
05543010 ILLINOIS RIVER AT SENECA, IL
LOCATION - Lat 41°17'59.6", long 88°36'51.1" referenced to North American Datum of 1983, in NW 1/4 SE 1/4 SE 1/4 sec.26, T.33 N., R.5 E., LaSalle County, IL, Hydrologic Unit 07120005, on concrete mooring dolphin in river at Seneca, 0.3 miles downstream from highway 170, 5.9 miles upstream from Marseilles Lock and Dam, 20 miles downstream from Kankakee River, and at mile 252.5.
DRAINAGE AREA - 8,215 mi².
REVISIONS HISTORY - Revisions: Gage datum was updated to 462.58 ft NAVD88 on May 30, 2023, based on GNSS Level II survey using GEOID18.
SURFACE-WATER RECORDS
PERIOD OF RECORD -
SURFACE-WATER DISCHARGE AND STAGE
  STAGE: July 2013 to current.
SURFACE WATER QUALITY
CHEMICAL: April 1979 (bed material analysis).
WATER TEMPERATURE: October 2012 to current.
SPECIFIC CONDUCTANCE: June 2013 to current.
DISSOLVED OXYGEN: June 2013 to current.
PH: June 2013 to current.
TURBIDITY: June 2013 to current.
NITRATE: July 2013 to current.
BLUE-GREEN ALGAE: June 2013 to current.
CHLOROPHYLL: June 2013 to current.
GAGE - Water-stage recorder, satellite telemeter, crest-stage gage, and water-quality monitor. Datum of gage is 462.58 ft above NAVD of 1988
EXTREMES FOR PERIOD OF RECORD -
STAGE: Maximum gage height, 33.25 ft., May 19, 2020; minimum, 18.99 ft, December 2, 2018.
WATER TEMPERATURE: Maximum, 32.7 oC, July 20, 2013; minimum, 0.0 oC, several days in most years.
SPECIFIC CONDUCTANCE: Maximum, 1390 uS/cm at 25oC, December 27, 2013; minimum, 332 uS/cm at 25oC, Sept. 28, 2019.
DISSOLVED OXYGEN: Maximum, 15.4 mg/L, February 28, 2015; minimum, 2.92 mg/L, Sept. 5, 2021.
PH: Maximum, 8.9 standard units, April 30, 2018; minimum, 7.2 standard units, June 2-3, 2016.
TURBIDITY: Maximum, 1057 FNU, July 12, 2021; minimum, 0.01 FNU, Nov. 9, 2020.
NITRATE: Maximum, 10.8 mg/L, June 12, 2014; minimum, 1.92 mg/L, February 25, 2014.
BLUE-GREEN ALGAE: Maximum, 121 ug/l, November. 21, 2014; minimum, 0.00 ug/l, several days during 2014.
CHLOROPHYLL: Maximum, 72.8 ug/l, Aug. 06, 2019; minimum, 1.32 ug/l, Nov. 8, 2017.