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Web Portal Changes: The Advanced Hydrologic Prediction Service (AHPS) hosted at will be replaced by the National Water Prediction Service (NWPS), with a target of March 2024. Existing AHPS content and features will be preserved and expanded within NWPS.

Experimental National Water Center Products: Flood Inundation Mapping services are now available for 10% of the U.S. population. Please visit for more information. The National Hydrologic Discussion, Area Hydrologic Discussion, Flood Hazard Outlook, and real-time geospatial services depicting River Forecast Center and National Water Model forecasts, continue to be accessible via the URL above, as described in the StoryMap here.

Hydrograph River at a Glance Download
Mainstream Deep Tunnel at McCook Reservoir Stage (ft)Observed: -244.63 ft at 7:00AM Sep 23, 2023Observed: -259.11 ft at 7:00AM Sep 24, 2023Observed: -272.29 ft at 7:00AM Sep 25, 2023Observed: -269.2 ft at 7:00AM Sep 26, 2023Observed: -243.53 ft at 7:00AM Sep 27, 2023Metropolitan Water Reclamation DistrictMCCI2(plotting HGIRZ) Graph Created (5:10AM Sep 28, 2023)ObservedLatest observed value: -243.53 ft at 7:00 AM CDT 27-Sep-2023.
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Tabular Data (UTC)
Tabular Data (CDT)
XML Data
RSS Files
Datum: NAVD88
NOTE: Graphical forecasts are not available for the Mainstream Deep Tunnel at McCook Reservoir. During times of high water, forecast crest information can be found in the text products.
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Downstream Gauge Downstream Gauge - at Lemont
Flood Categories (in feet)
Not Available

Historic Crests
(1) -35.00 ft on 05/06/2019
(2) -38.90 ft on 05/21/2020

(P): Preliminary values subject to further review.

Recent Crests
Currently none available.

Low Water Records
Currently none available.
Zoom Level:16
KML Image
Gauge LocationGauge Map Marker
Latitude/Longitude Disclaimer: The gauge location shown in the above map is the approximate location based on the latitude/longitude coordinates provided to the NWS by the gauge owner.
Flood Impacts & Photos Collapse
If you notice any errors in the below information, please contact our Webmaster
-40 McCook Reservoir reaches 100 percent of full storage. Combined sewer overflow event likely.
-95 McCook Reservoir reaches 75 percent of full storage. Combined sewer overflow event possible.
-155 McCook Reservoir reaches 50 percent of full storage.
-215 McCook Reservoir reaches 25 percent of full storage.
-280 McCook Reservoir is empty, 0 percent of full storage.
About This Location Collapse

Latitude: 41.777500° N, Longitude: 87.836600° W, Horizontal Datum: NAD83/WGS84

River Stage
Reference Frame
Gauge Height Flood Stage Uses
NWS stage 0 ft Not Available Interpreting hydrographs and NWS watch, warnings, and forecasts, and inundation maps
Vertical Datum Elevation
(gauge height = 0)
(gauge height = flood stage)
Elevation information source
NAVD88 579.20 529.20 Survey grade GPS equipment, FEMA flood plain maps, newer USGS topographic maps
NGVD 29 579.48 529.48 Older USGS topographic maps, NGVD29 benchmarks
MSL Not Available Not Available Older USGS topographic maps, MSL benchmarks
Other 0.0 -50.0 Chicago City Datum
Additional Information Collapse
McCook Reservoir Webcam
TARP Reservoir Storage Levels
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Hydrologic Resources Additional Resources
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The National Weather Service prepares its forecasts and other services in collaboration with agencies like the US Geological Survey, US Bureau of Reclamation, US Army Corps of Engineers, Natural Resource Conservation Service, National Park Service, ALERT Users Group, Bureau of Indian Affairs, and many state and local emergency managers across the country. For details, please click here.
NWS Information
National Weather Service
Chicago Weather Forecast Office
333 W. University Dr.
Romeoville, IL 60446
(815) 834-1435
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Page last modified: 2-Nov-2020 7:29 PM
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