Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2015

MAY

1973

JUN

1952

JUL

1947

AUG

1947

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2016

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

19731935

JUN

19521935

JUL

19471934

AUG

19471934

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

2017

JAN

1946

1935

FEB

1952

1936

MAR

19521935

APR

19731935

MAY

19731935

JUN

19521935

JUL

19471934

AUG

19471934

SEP

19471934

OCT

19451934

CHART DATUM 243.3 FEET (74.2 METERS)

Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

+ 6

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5+ 1.8

2015

MAY

1986

JUN

1986

JUL

1986

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2016

JAN

1987

FEB

1987

MAR

1986

APR

1985

MAY

1986

1934

JUN

1986

1934

JUL

1986

1934

AUG

1986

1934

SEP

1986

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1934

2017

JAN

19871935

FEB

1987

1936

MAR

1986

1934

APR

19851934

MAY

1986

1934

JUN

1986

1934

JUL

1986

1934

AUG

1986

1934

SEP

1986

1934

OCT

1986

1934

CHART DATUM 569.2 FEET (173.5 METERS)

Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2015

MAY

1986

JUN

1986

JUL

1986

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2016

JAN

1986

FEB

1986

MAR

1986

APR

1986

MAY

1986

1934

JUN

1986

1934

JUL

1986

1934

AUG

1986

1934

SEP

1986

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1964

2017

JAN

19861936

FEB

19861926

MAR

1986

1934

APR

19861926

MAY

1986

1934

JUN

1986

1934

JUL

1986

1934

AUG

1986

1934

SEP

1986

1934

OCT

1986

1934 CHART DATUM 572.3 FEET (174.4 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH 

Superior

601.74

183.41

601.97183.48602.62183.68

1986

599.48182.72

1926

601.25

183.26

MichHuron

579.59

176.66

579.95176.77

581.46

177.23

1986

576.15

175.61

1964

578.67176.38

St.

Clair

575.69175.47575.75175.49576.84175.82

1986

571.92174.32

1926

574.28175.04

Erie

572.97174.64572.83

174.60

574.08174.98

1985

568.83173.38

1934

571.59174.22

Ontario

247.21

75.35

246.42

75.11

248.20

75.65

1973

242.88

74.03

1935

245.67

74.88

APRIL MEAN LAKE LEVELS

(IGLD 1985)

* 2017 Ft.

M.

2016 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional** Average, Maximum and Minimum for period 1918-2016

1985

1985

1973 1973

1936

1934

1926 1934

LAKE ONTARIO

LAKE ERIE

LAKE ST. CLAIR

LEGEND

LAKE LEVELS

RECORDEDPROJECTEDAVERAGE **MAXIMUM **MINIMUM **

The levels on the hydrographs are shown inboth feet and meters above (+) or below (-) Chart Datum. Chart Datum, also known as Low Water Datum, is a reference plane on each lake to which water depth and Federal navigation improvement depths on navigation charts are referred.All elevations and plots shown in this bulletin are referenced to International Great Lakes Datum 1985 (IGLD 1985). IGLD 1985 has its zero base at Rimouski, Quebec near the mouth of the St. Lawrence River (approximate sea level).
Information

Recorded water levels in this bulletin are derived from a representative network of water level gages on each lake 

(see cover map). Providers of these data are the U.S. Department of Commerce, NOAA, National Ocean Service, 

and Integrated Science Data Management, Department of Fisheries and Oceans, Canada. The Detroit District, 

Corps of Engineers and Environment Canada derive historic and projected lake levels under the auspices of the 

Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data.

This bulletin is produced monthly as a public service. The Corps also, on a weekly basis publishes online the Great 

Lakes, Connecting Channels and St. Lawrence River Water Levels and Depths, which provides a forecast of depths 

in the connecting rivers between the Great Lakes and the International Section of the St. Lawrence River. This 

Monthly Bulletin of the Lake Levels for the Great Lakes may be obtained free of charge by writing to the address 

shown on the front cover, by calling (313) 226-6442 or emailing hhpm@usace.army.mil. Notices of change of 

address should include the name of the publication. This information is available on the internet at 

http://www.lre.usace.army.mil/Missions/GreatLakesInformation.aspx.

Great Lakes Basin Hydrology

April 2017

According to preliminary estimates, precipitation during the month of April was well above average for the Great 

Lakes basin. Lake Erie received 17% more precipitation than average, Lake Superior received nearly 50% more 

than average, while Lakes Michigan-Huron and Ontario received 62% and 54% more than average April 

precipitation, respectively. As a result of the large amounts of precipitation, water supply to all lakes was well above 

average. All lakes’ outflows remained above average throughout April.

All of the lakes were above their long-term average (LTA) water levels for the month of April. All lakes are 

experiencing their seasonal rise. Lake Superior rose about 1 inch from March to April. Lakes Michigan-Huron, St. 

Clair, and Erie each rose 5 to 7 inches, while Lake Ontario rose 14 inches. The mean April Lakes Superior and 

Michigan-Huron levels were both below last year’s April levels. Lakes Erie and Ontario, on the other hand, were 2 

and 9 inches above last year’s levels, respectively.

PRELIMINARY PRECIPITATION (INCHES)

BASIN

April 12-Month Comparison

2017 Average Diff. % of 

Average

Average Last 

12 months 

Average Diff. % of 

(1900-2014) (1900-2014) Average

Superior 2.99 2.03 0.96 147 33.25 30.52 2.73 109

Michigan-Huron 4.32 2.66 1.66 162 33.29 32.57 0.72 102

Erie 3.74 3.20 0.54 117 34.33 35.65 -1.32 96

Ontario 4.53 2.94 1.59 154 33.75 35.87 -2.12 94

Great Lakes 3.57 2.59 0.98 138 33.07 32.76 0.31 101

 LAKE April Net Basin Supplies1 (cfs) April Outflows2 (cfs)

2017

Average

(1900-2008) 2017

Average3

(1900-2008)

Superior 240,000 150,000 77,000 68,000

Michigan-Huron 422,000 284,000 212,000 182,000

Erie 95,000 67,000 245,000 207,000

Ontario 126,000 93,000 269,000 251,000

Notes: Values (excluding averages) are based on preliminary computations; cfs denotes cubic feet per second.

1 Net basin supply is the net result of precipitation falling on the lake, runoff from precipitation falling on the land which flows to 

the lake, and evaporation from the lake. Negative net basin supply denotes evaporation exceeded runoff and precipitation. 

The net total supply can be found by adding the net basin supply and the outflow from the upstream lake.

2 Does not include diversions.

3 Lake Ontario average water supplies and average outflows are based on period of record 1900-2005