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Great Lakes Water Management

Great Lakes Water Level Data

Graphics are representations, click the links for the most updated levels.
Long term average, maximum, and minimum Great Lakes water levels
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Metric Units
Coordinated monthly mean water levels
English Units
Metric Units

 

Graphics are representations, click the links for the most updated levels.
Daily Great Lakes Water Levels
Daily Great Lakes Water Levels in English and Metric Units 
Great Lakes Water Levels Report
Metric Units
English Units

 

Links navigate to a separate website managed by the National Oceanic and Atmospheric Administration.

 

Great Lakes Basin Conditions

Latest monthly hydrology and water level summaries
Information on the month's net basin supply and precipitation. These summaries are also included in the publication of the Monthly Bulletin of Great Lakes Water Levels. Monthly Water Level Summaries provide details on the water levels for each Great Lake and include observations on how water level changes relate to recent hydrological conditions.
Last month hydrology summary
Last month water level summary

 

Recent net basin supply, evaporation, precipitation, and runoff conditions.

Net Basin Supply

Net basin supply (NBS) is the primary driver of Great Lakes water levels. NBS represents the total contribution of water to each lake, excluding inflows from upstream lakes, outflows to downstream lakes, and diversions into or out of the lakes, as shown in the graphic above. In other words, NBS represents the net influence of precipitation over the lake, runoff from a lake’s watershed into the lake, and evaporation from the lake’s surface.

NBS relative to long term average NBS for the past five years

Precipitation
Basin-wide precipitation, relative to long term average, for the past five years

Evaporation

Evaporation is typically highest during the late fall and early winter, when the air temperature is much colder than the surface water temperature. Evaporation is difficult to estimate, due to the lack of observations across the lakes' surface.

Simulated evaporation rates from the Large Lake Thermodynamic Model, relative to average, for the past five years

Runoff

Runoff to the Great Lakes is typically highest during the spring, when melting snow combines with liquid precipitation, leading to increased streamflow.

Simulated runoff rates from the Large Basin Runoff Model, relative to average, for the past five years

Hydrometeorological conditions in the Great Lakes
Snow Water Equivalent
Snow water equivalent data from NOAA's National Operational Hydrologic Remote Sensing Center (NOHRSC) aggregated to Great Lakes basins
Ice Cover
Recent and historical ice cover compiled from data from NOAA's Great Lakes Environmental Research Laboratory (GLERL)
Surface Water Temperature
Recent and historical surface water temperatures compiled from data provided by NOAA's Great Lakes Environmental Research Laboratory (GLERL)
NBS Components: Precipitations, Evaporation, and Runoff

Net basin supply (NBS) is the primary driver of Great Lakes water levels. NBS represents the total contribution of water to each lake, excluding inflows from upstream lakes, outflows to downstream lakes, and diversions into or out of the lakes, as shown in the graphic to the right. In other words, NBS represents the net influence of precipitation over the lake, runoff from a lake's watershed into the lake, and evaporation from the lake's surface.

This tab shows trends in precipitation, evaporation, and runoff from 1950 to 2022 for Lakes Superior, Michigan-Huron, Erie, and Ontario. There are four sections, one for each lake, that provide a table summarizing monthly and annual trends, a monthly graphic that displays values of precipitation, evaporation, and runoff by month from 1950 to 2022, and an annual graphic that shows the accumulated precipitation, evaporation, and runoff in each year from 1950 to 2022. A black line is plotted to help represent the patterns and trends in the data on a monthly and annual temporal scale. These trends are based on the data shown from 1950 to 2022 and may not be reflective of future trends. See Data Description below for more information.

Lake Superior
Monthly NBS components
Annual NBS components
 

Precipitation Evaporation Runoff
Precipitation during April shows an increasing trend since the 1980s through the recent period and was noticeably high in April 2022. Evaporation during the winter months has shown an increasing trend since the 1950s, and was particularly high in January of 2022. Runoff in May 2022 was very high, contributing to the overall increasing trend seen over the last two decades.
After two years of lower annual precipitation, 2022 was higher. On average, annual accumulated evaporation has been increasing over the last 7 decades. 2022 runoff rates were higher than the previous two years.

Lakes Michigan-Huron
Monthly NBS components
Annual NBS components

Precipitation Evaporation Runoff
February to May 2022 had higher precipitation than in 2021.  Evaporation during July and August has shown an increasing trend in the last 3 decades. January 2022 experienced a major increase in evaporation. Runoff increased in the Spring and stayed relatively consistent otherwise. 
In 2022, annual precipitation was below the higher rates of the preceding 5 years. Annual accumulated evaporation has shown an increasing trend over the last 4 decades. Over the last two decades, annual runoff rates show an increasing trend, but the past two years have been lower.

Lake Erie
Monthly NBS components
Annual NBS components
Precipitation Evaporation Runoff
October had a significant decrease in precipitation in 2022.  Evaporation rates during September show a decreasing trend in the last two decades, despite higher rates in recent years. Runoff during December and January has been lower in recent years and indicates a slight decreasing trend. 
Precipitation in 2022 was lower than the past 5 years.  Evaporation does not show signs of any trend on the annual timescale since 1950. After several years of high runoff, rates have been lower in the past few years.

Lake Ontario
Monthly NBS components
Annual NBS components
Precipitation Evaporation Runoff
July and October saw a drop in precipitation in 2022.  Evaporation in May, June. July, and August, shows a slight increasing trend in the last two to three decades. Lower runoff rates were experienced in January and October 2022 than in recent years.
Since the 1970s, high annual rates of precipitation have been more frequent. Annual rates of evaporation in the last two decades have been generally higher and show a slight increasing trend. After a few years with high runoff, recent years have had lower runoff rates. 

Data Information
NBS Component Data

Precipitation data is from the Great Lakes Seasonal Hydrological Forecasting System.

Evaporation data is modeled using the Large Lake Thermodynamics Model (LLTM).

  • Croley, T. E. (1989). Verifiable evaporation modeling on the Laurentian Great Lakes. Water Resources Research25(5), 781-792.

Runoff data is modeled using the Large Basin Runoff Model (LBRM).

  • Croley, T. E. (2002). Large basin runoff model. Mathematical models in watershed hydrology, 717-770.

Graphics inspired by Hunter et al. 2015.

  • Hunter, T. S., Clites, A. H., Campbell, K. B., & Gronewold, A. D. (2015). Development and application of a North American Great Lakes hydrometeorological database—Part I: Precipitation, evaporation, runoff, and air temperature. Journal of Great Lakes Research41(1), 65-77.

The black lines in the graphics are calculated using a locally weighted regression.

All NBS graphics are scheduled to be updated every spring.

This tab shows historical surface water temperatures and ice cover for Lakes Superior, Michigan, Huron, Erie, and Ontario. There are five sections, one for each lake, that provide a table describing past conditions, a graphic showing monthly and annual average surface water temperatures, and a graphic showing monthly and annual maximum ice cover. Average surface water temperatures are shown over the period 1995-2022 and ice cover is shown from November 1972 to June of 2023. Please note that the years on the annual plots refer to ice years, which starts in November or December of the previous year. For example, the ice year of 2015, would be from November 2014 to June 2015.

Lake Superior
Monthly & annual surface water temperature
Monthly & annual ice cover
Surface Water Temperatures Ice Cover
Surface water temperatures in the summer and fall months experienced a large decrease from 2021 to 2022. Ice cover in February and March was much lower in 2023 than in the previous year. 
Surface water temperatures in 2022 were lower than they were in recent years.  Ice cover in winter 2023 was under 25%, which was much lower than the previous winters of 2022 and 2021.

Lake Michigan
Monthly & annual surface water temperature
Monthly & annual ice cover
Surface Water Temperatures Ice Cover
Surface water temperatures underwent a large decrease from 2021 to 2022 in June and October.  Over the past winter, ice cover was higher in December but lower in all other months.
Surface water temperatures in September 2022 were high, similar to 2021.  The most recent years with significant ice cover were during the winters of 2013-2014 and 2014-2015.

Lake Huron
Monthly & annual surface water temperature
Monthly & annual ice cover
Surface Water Temperatures Ice Cover
September was the only month that had a higher surface water temperature in 2022 than in 2021.  Ice cover in January, February, and March were much lower in 2023 than in 2022. 
Annual surface water temperatures have remained relatively consistent over the past two decades.  There is substantial variability in ice cover throughout the period of record (1972-present).

Lake Erie
Monthly & annual surface water temperature
Monthly & annual ice cover
Surface Water Temperatures Ice Cover
Surface water temperatures in October 2022 were much lower than in 2021.  Lake Erie is the shallowest Great Lake, and therefore usually experiences higher ice cover from year to year.
Surface water temperatures in November have been higher in recent years.  Ice cover on Lake Erie was much lower in 2023 than in the previous two years.

Lake Ontario
Monthly & annual surface water temperature
Monthly & annual ice cover
Surface Water Temperatures Ice Cover
Surface water temperatures in November have been higher in recent years.  As a result of Lake Ontario's depth and location, generally low ice cover is seen from year to year.
Annual surface water temperatures have been relatively consistent over the past three years on Lake Ontario. Ice cover was much lower in 2023 compared to 2022.

Data Information
Surface Water Temperatures and Ice Cover Data

Surface water temperature data is provided at a daily time step and comes from http://coastwatch.glerl.noaa.gov/statistic/. The period of record is from October 1994 to present.

Ice cover data is also provided on a daily time step and can be found at https://www.glerl.noaa.gov/data/ice/#historical (daily averages by lake). The period of record is from November 1972 to June 2023. Please note that years on the annual plots refer to "Ice Years", which starts in November or December of the previous year. For example, the ice year of 2015, would be from November 2014 to June 2015.

Graphics inspired by Hunter et al. 2015.

  • Hunter, T. S., Clites, A. H., Campbell, K. B., & Gronewold, A. D. (2015). Development and application of a North American Great Lakes hydrometeorological database—Part I: Precipitation, evaporation, runoff, and air temperature. Journal of Great Lakes Research41(1), 65-77.

Surface water temperature and ice cover graphics are scheduled to be updated every spring

Great Lakes Outflows

The outflows from two of the five Great Lakes (Lake Superior and Lake Ontario) are regulated by control structures. These outflows are varied in accordance with their respective regulation plans.

The outflows from Lakes Michigan-Huron and Erie are not regulated, but rather, are controlled exclusively by the hydraulic characteristics of their outlet rivers.

Lake Superior

Outflows from Lake Superior are regulated near the twin cities of Sault Ste. Marie, Michigan and Ontario. Outflows are controlled by three hydropower plants and a 16-gate control structure called the Compensating Works. The outflow is established on a monthly basis by the International Lake Superior Board of Control (ILSBC). The outflow is set in accordance with the current regulation plan, Plan 2012.

http://ijc.org/en_/ilsbc/International_Lake_Superior_Board_of_Control 
Lake Ontario

Outflows from Lake Ontario are established on a weekly basis by the International Lake Ontario-St. Lawrence River Board (ILOSLRB). The principle control structure is the Moses Saunders Dam. The Lake Ontario outflow is set in accordance with the current regulation plan, Plan 2014.

http://ijc.org/en_/islrbc
The Measurement of Flows in the Great Lakes Connecting Channels and the International Section of the St. Lawrence River

The discharge of a river is defined as the volume of water flowing past a particular point in unit time. The US Army Corps of Engineers collects flow data (discharge) in the Connecting Channels (the St. Marys River, the St. Clair River, the Detroit River, and the Niagara River) and the international section of the St. Lawrence River to develop and verify ratings for water level gauges, to analyze hydraulic structures, and to calibrate hydraulic models. Discharge data are also used operationally in navigation, hydropower production, lake regulation, water level forecasting, water apportionment, monitoring of compliance with agreements and treaties and in a wide range of studies.

Detailed information regarding the collection and use of flow or discharge data can be found in the report Discharge Measurement Procedures on the Great Lakes Connecting Channels and the International Section of the St. Lawrence River, prepared by the Coordinating Committee of Great Lakes Basic Hydraulic and Hydrologic Data in October 1991 as well as Update Articles from July and August 1992.

Download discharge measurements via comma separated value formatted text file. 
Learn more about flows on the Great Lakes connecting channels and how they are measured

 

Download the multivolume Hydraulic Discharge Measurements and Regimen Changes on the Great Lakes Connecting Channels and the International Section of the St. Lawrence River report.

  • Main Report & Appendix A
  • Appendix B Chronologic Summaries of Construction and Dredging
  • Appendix C Table Summaries of Discharge Measurements

Email hhpm@usace.army.mil for more information on discharge measurements.

The St. Clair River is a naturally occurring dynamic river system which plays a role in conveying water from Lake Huron to Lake St. Clair and eventually Lake Erie. As such, any change in the shape of the river can have an effect on the level of the Great Lakes. Sediment entering the St. Clair River from Lake Huron, dredging the navigation channel, ice jams and other natural processes can all result in changes to the rivers ability to move water through the system. The U.S. Army Corps of Engineers Detroit District monitors changes in the St. Clair River by measuring the shape, or bathymetry, of the river and computing how the changes affect the amount of water that can pass through the system.

Additional information is available upon request at HHPM@USACE.ARMY.MIL.

Great Lakes Water Level Forecast

Great Lakes Futures Scenario

This section is not an official forecast of Great Lakes water levels. Rather, this product is meant to illustrate outcomes that would occur under historical weather and water supply condition, with scenarios chosen based on similarities to recent conditions. For the official forecast, please see our Monthly Bulletin of Great Lakes Water Levels. This tool has been predominantly used to show the possible range of water levels in the upcoming year based on historical hydrologic conditions and water supplies. Beginning in 2021, we will be modifying our scenarios to account for different time periods based on the scenario that is chosen. 

Water levels follow a seasonal cycle where during the fall and early winter, the lakes generally decline due to an increase in evaporation as temperatures decline and cold air moves over the relatively warm lake waters. In the spring and early summer, water levels typically rise due to increased precipitation and enhanced runoff from snowmelt. We refer to the combined effect of precipitation over the lake, evaporation from the lake, and runoff to the lake as Net Basin Supply (NBS). This edition of the Water Level Future Scenarios incorporates the projection of water levels if NBS conditions approximated those that occurred in the 12 months during and after the 8 ‘strongest’ El Nino events. The effects of the 8 NBS sequences are represented by the purple plume.  Three of the ‘strongest’ El Ninos occurred in 1958, 1983, and 1998, and their hypothetical impacts on future water levels are represented by the green, blue, and pink lines.  The gray shaded area on the plot represents the full range of possible outcomes using historical sequences of NBS from 1900 through 2022.  The most recent coordinated 6-month forecast is also shown for comparison.

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