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Levels & Hydrology Section: Home | Levels | Hydrology | Flows

What's New
Groups urge adoption of Lake Ontario water-level plan
Democrat & Chronicle (12/7)
A broad-based coalition of conservation, sporting, business and other groups has launched an advertising and social media campaign to rally support for a new water-level plan for Lake Ontario.

Coalition urges adoption of regulation plan for Lake Ontario, St. Lawrence River
Watertown Daily Times (11/13)
A coalition of elected officials and environmental and business interests is urging the U.S. and Canadian governments to stop delaying the implementation of a new plan to regulate the flows of Lake Ontario and the St. Lawrence River.

Watching ships pass on the Welland Canal
The Cornwall Standard-Freeholder (10/15)
Visitors to the Welland Canals Centre at Lock 3 in St. Catharines, Ont., and Lock 7 in Thorold, Ont., can view a historic example of engineering: Canadaís version of the Panama Canal.

As barriers disappear, fish are darting up Menomonee River
Milwaukee Journal Sentinel (10/15)
Even though restoration of the Menomonee River in Milwaukee, Wis., won't be completed for a month, fish of all sizes are already swimming through the construction zone to try out new rock-lined riffles and pools.

Ballville Damís fate takes on new urgency in wake of water crisis
The Toledo Blade (8/17)
Toledoís recent water crisis heightened concern from some who want to make sure the proposed removal of the Sandusky Riverís Ballville Dam doesnít worsen algal blooms.

Guess who's dumping in Lakes Michigan and Huron? It's Lake Superior
MLive (8/6)
There's a lot of dumping going on right now into Lake Michigan and Lake Huron. But it's all good news. Lake Superior is dumping water into Lakes Michigan and Huron, and lots of it.

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Profile of Great Lakes-St. Lawrence System Overview
The Great Lakes system is a chain of lakes and connecting channels descending like a series of steps toward the Atlantic Ocean. Lake Superior, located at the top of the chain, is about 183 metres (601.7 feet) above sea level, while Lake Ontario stands at about 74.7 metres (245.1 feet). (Select the adjacent image, courtesy of the U.S. Army Corps of Engineers, Detroit District, for a larger view of the Great Lakes-St. Lawrence system's profile.)

Water from Lake Superior flows into Lake Huron through the St. Marys River. Since Lake Michigan and Lake Huron are connected by the broad and deep Straits of Mackinac and stand at virtually the same elevation, they are often referred to as one lake hydrologically; that is, Lakes Michigan-Huron. From Lakes Michigan-Huron, water flows through the St. Clair River, Lake St. Clair and the Detroit River into Lake Erie. Lake Erie discharges through the Niagara River and the Welland Canal into Lake Ontario. The portion of flow diverted to Lake Ontario through the Welland Canal is relatively small (about 4 to 5 percent of the total Lake Erie outflow). Water from Lake Ontario flows to the Atlantic Ocean through the St. Lawrence River. The average St. Lawrence River flow, recorded at Cornwall, Ontario, during the period 1900-95, is 6,910 cubic metres (244,000 cubic feet) per second. This average outflow is relatively small (less than 1 percent per year) in comparison to the total volume of water contained in the system.

Only the outflows from lakes Superior and Ontario are regulated via control structures, and may be varied within limits in accordance with their respective regulation plans. The outflows from lakes Michigan-Huron and Erie are controlled exclusively by the hydraulic characteristics of their outlet rivers.

The immense storage capacities of the Great Lakes, in combination with their restricted outflow capacities, allows the lakes to absorb large variations in water supplies, while maintaining remarkably steady outflows compared with other large rivers. For example, the highest St. Lawrence River flow is only 2.3 times greater than its lowest rate. In contrast, the Mississippi River at St. Louis, Missouri, has a maximum flow about 30 times its minimum.

Because of the size of the Great Lakes and the limited discharge capacities of their outlet rivers, extremely high or low levels can persist for a considerable time, even when water supplies change significantly.

David Schweiger
U.S. Army Corps of Engineers, Detroit District

Charles F. Southam
Environment Canada-Ontario Region, Environmental Services Branch

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General Resources
GLIN: Compare snow melt (snow water equivalent) for the upper Great Lakes basin: 1997-2000
From the summer of 1997 to today, water levels on the middle Great Lakes have fallen from near record highs to near record lows. This decline is nearly 3.5 feet on lakes Michigan, Huron, St. Clair and Erie. This trend is forecasted to continue for the foreseeable future due in part to the fact that the drainage basins for lakes Superior and northern Michigan and Huron (the headwaters for the Great Lakes) have had one of the driest winters on record. Snowmelt runoff is a key component in replenishing groundwater and tributary stream flows into the Great Lakes.

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Current Conditions
Lake Superior Outflow
International Lake Superior Board of Control
Provides news releases from the board regarding outflow from Lake Superior.

Significant Events
U.S. Army Corps of Engineers (USACE), Detroit District
The outflows of lakes Superior and Ontario for the last month, along with other significant events for the current month are updated daily.

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Forecasted Conditions
Lake Superior Outflow
International Lake Superior Board of Control
Provides news releases from the board regarding outflow from Lake Superior.

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Great Lakes Basin Hydrology Home Page
U.S. Army Corps of Engineers (USACE), Detroit District
Includes recent monthly flows and the average flow for the period 1900-1989.

Great Lakes Monthly Hydrologic Data (1860-1990)
National Oceanic and Atmospheric Administration (NOAA), Great Lakes Environmental Research Laboratory (GLERL)
Historical monthly flows for the connecting channels--St. Marys, St. Clair, Detroit and Niagara rivers--and the St. Lawrence River and diversion are available from various original sources.

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Related Resources
GLIN: Agencies and Organizations, Hydrology
GLIN: Factors Affecting Great Lakes-St. Lawrence System Flows
GLIN: Great Lakes-St. Lawrence Hydrology
GLIN: Great Lakes-St. Lawrence Water Levels
GLIN: St. Marys River Flows
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 18, 2014
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