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  Great Lakes-St. Lawrence Hydrology
What's New | Weekly Levels Forecast | Overview | Datums | Education
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Levels & Hydrology Section: Home | Levels | Hydrology | Flows

What's New
Meet two cool buoys on the Great Lakes
WBFO Ė Buffalo, NY (9/14)
A pair of buoys on Lake Michigan, which gather data and photos, and share them over Twitter, shared their story in a tongue-and-cheek interview.

3 ways high water levels are good, 2 not so much
MLive (6/3)
Whatever your perspective, experts reassure us, water levels in West Michigan are cyclical over the long term. While they may have positive or negative impacts, the levels aren't permanent.

High water levels shrink beaches, help shippers, boaters, ecology
MLive (6/3)
After a couple snowy winters coupled with decent rainfall amounts in warmer months, Muskegon, Mich., river, stream and lake levels are the highest they've been in many years.

New project focuses on watersheds, green infrastructure
Great Lakes Echo (1/21)
A new project from the Great Lakes Commission is hoping to use green infrastructure to reconnect the natural Great Lakes watershed.

Great Lakes water levels to hit 20 year high
WDET - Detroit, MI (1/20)
Great Lakes water levels are predicted to rise nine inches above average this summer.

St. Clair River ice jamming remains a concern
Blackburn News (1/14)
With Lake St. Clair essentially frozen over, ice flows drifting downriver from Lake Huron are building up. The jams are impacting ferry service.

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Weekly Water Levels Forecast
New! Update for Friday April 15, 2015 (includes data summary)

Weather conditions: The Great Lakes Basin received precipitation several days last week, which contributed to the slightly above average month to date precipitation total of 1.02 inches. Temperatures were colder to start the week throughout the Great Lakes Basin and gradually warmed up later in the week. Heading into the weekend, expect clear skies and warm temperatures throughout the basin. That trend will continue throughout the lower basin heading into the workweek, while some precipitation and lower temperatures are expected in the Lake Superior Basin on Monday.

Lake Level Conditions: Lake Superior is 1 inch higher than it was a month ago. Lakes Michigan-Huron, St. Clair, Erie and Ontario are in the midst of their seasonal rise and are 7 to 8 inches above what they were a month ago. All lakes are above their average levels of a year ago; Lake Superior is 2 inches higher, Lakes Michigan-Huron, St. Clair, and Erie are 10 to 15 inches higher, and Lake Ontario is 20 inches higher than they were at this time last year. All of the lakes are forecasted to rise 2 to 4 inches over the next 30 days. See the Daily Levels page for more water level information.

Forecasted outflows / channel conditions: Lake Superiorís outflow through the St. Maryís River is projected to be above average for the month of April. Lake Michigan-Huronís outflow into the St. Clair River and Lake St. Clairís outflow into the Detroit River are expected to be above average in April. Moreover, the April outflow of Lake Erie into the Niagara River is forecasted to be above average, and outflow of Lake Ontario into the St. Lawrence River is predicted to be above average in April.

Alerts: Official records are based on monthly average water levels and not daily water levels. Users of the Great Lakes, connecting channels and St. Lawrence River should keep informed of current conditions before undertaking any activities that could be affected by changing water levels. Mariners should utilize navigation charts and refer to current water level readings.

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Carved by glaciers, the Great Lakes-St. Lawrence River system is a series of steps that drains from Lake Superior in the west to the Atlantic Ocean in the east. Covering more than 94,000 square miles, the Great Lakes and their connecting channels form the largest fresh, surface water system on earth, holding about 18 percent of the world's supply.
Ever since the last glaciers retreated about 10,000 years ago, the system's water levels and outflows have been fluctuating, affecting the lakeshore environment and human activities. Unlike oceans, where ebbs and tides are constant and predictable, Great Lakes water level fluctuations are almost never regular, nor can their levels be predicted accurately in the long term. This is because the many factors affecting Great Lakes water levels and flows are never constant and likely can not be predicted accurately in the long term.
The major influences on Great Lakes hydrology are weather and climate, which affect the balance of water in the Great Lakes and their connecting channels. Water enters the system as precipitation, runoff (including snowmelt) from the surrounding land, and groundwater inflow. Water leaving the system consists of evaporation from the water's surface, groundwater outflow, consumptive uses and diversions.
The GLIN hydrology section discusses these factors and links to resources from many relevant agencies. We hope that an understanding of the Great Lakes system's dynamics will promote living in harmony with one of the most precious natural resources of this planet.
Coordinating Committee Co-chairs:
John Kangas
U.S. Army Corps of Engineers, Great Lakes and Ohio River Division
Peter Yee
Environment Canada, Great Lakes-St. Lawrence Regulation Office

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Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data

Datums - explanation of datums used for water levels and navigational charts
Department of Fisheries and Oceans, Canadian Hydrographic Service

Establishment of International Great Lakes Datum 1985
Department of Fisheries and Oceans, Canadian Hydrographic Service

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TEACH Great Lakes: Water Levels
Water levels are part of the ebb and flow of nature. Learn about the three types of water level fluctuations, how levels are measured on the Great Lakes, and what's causing the recent drop.

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Boundary Waters Treaty
United States and Canada, 1909

Great Lakes Charter

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Great Lakes Water Levels Home Page
U.S. Army Corps of Engineers (USACE), Detroit District
A regularly updated page of links to information on Great Lakes hydrology. Includes current conditions, recent water levels, forecasted levels, general news and information, multimedia, reference materials, and more!

Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data

Great Lakes Atlas
U.S. Environmental Protection Agency (EPA)
This Environmental Atlas and Resource Book is an excellent resource on the Great Lakes, including physical characteristics, natural processes, people, concerns, joint management and new directions (mirrored on Environment Canada's site).

Hydrologic Cycle Online Meteorology Guide
University of Illinois, Department of Atmospheric Sciences

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Related Resources
GLIN: Agencies and Organizations, Hydrology
GLIN: Environmental Research in the Great Lakes Region
GLIN: Great Lakes-St. Lawrence Water Flows
GLIN: Great Lakes-St. Lawrence Water Levels
GLIN: Weather and Climate in the Great Lakes Region

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CC Data This page was created under the guidance of the binational Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data. This symbol is used throughout the GLIN hydrology section to indicate data or references prepared under the auspices of the Coordinating Committee.


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Updated: December 15, 2017
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