NOTICE: This continuous water-quality monitor (water temperature, chlorophyll, and phycocyanin) will be discontinued on September 1, 2021, due to completion of the data collection portion of the Downstream Fate and Transport of Cyanobacteria and Cyanotoxins in the Raritan River Basin, New Jersey study.

SURFACE-WATER RECORDS
LOCATION.--Lat 40°28'30", long 74°34'33" referenced to North American Datum of 1983, Hillsborough Township, Somerset County, NJ, Hydrologic Unit 02030105, on left bank 30 ft downstream from highway bridge on Blackwells Mills Causeway at Blackwells Mills, 0.3 mi downstream from Six Mile Run, and 2.0 mi south of Borough of Millstone.
DRAINAGE AREA.--258 mi².
PERIOD OF RECORD.--June 1903 to December 1904 (gage heights only), August 1921 to current year. Monthly discharge only for some periods, published in WSP 1302. Published as "at Millstone" 1903-04.
REVISED RECORDS.--WSP 1552: 1924-25(M), 1926. WDR US-2011: 1999, 2007, 2010.
GAGE.--Water-stage recorder with telemetry. Concrete control since Nov 18, 1933. Datum of gage is 26.97 ft above NGVD of 1929. June 27, 1903 to Dec 31, 1904, non-recording gage at bridge 2.0 mi downstream at Millstone at different datum. Aug 4, 1921 to Aug 16, 1928, non-recording gage at present site and datum.
REMARKS.--Records good, except for estimated discharges and discharges greater than 2,000 ft³/s, which are fair. Inflow from and losses to Delaware and Raritan Canal upstream of station. Flow slightly regulated by Carnegie Lake, capacity, 310,000,000 gal and several smaller reservoirs, combined capacity, 49,800,000 gal.
EXTREMES FOR PERIOD OF RECORD.--Maximum discharge, 22,200 ft³/s, Aug 28, 1971, gage height, 18.68 ft, from high-water mark, maximum gage height, 21.24 ft, Aug 28, 2011, maximum discharge occurred during different floodplain conditions; minimum discharge, 5.0 ft³/s, Sep 16, 1923.

WATER-QUALITY RECORDS
PERIOD OF RECORD.--Water years 1962-69, 1973, 1976-80, 1991 to current year.
REMARKS.--Discrete water-quality data were collected as part of the New Jersey Ambient Surface-Water-Quality Monitoring Network.

Peak Flood Chart

National Weather Service flood stage for this gage is 9.0 ft.

Forecasts for this gage are issued by the National Weather Service routinely year-round.
Forecast information is available here.