Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2013

JUN

1952

JUL

1947

AUG

1947

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2014

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

1973

JUN

19521935

JUL

19471934

AUG

19471934

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

2015

JAN

1946

1935

FEB

1952

1936

MAR

19521935

APR

19731935

MAY

19731935

JUN

19521935

JUL

19471934

AUG

19471934

SEP

19471934

OCT

19451934

NOV

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

2013

JUN

1986

JUL

1986

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2014

JAN

1987

FEB

1987

MAR

1986

APR

1985

MAY

1986

JUN

1986

1934

JUL

1986

1934

AUG

1986

1934

SEP

1986

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1934

2015

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

NOV

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

2013

JUN

1986

JUL

1986

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2014

JAN

1986

FEB

1986

MAR

1986

APR

1986

MAY

1986

JUN

1986

1934

JUL

1986

1934

AUG

1986

1934

SEP

1986

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1964

2015

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

NOV

1986

1934

CHART DATUM 572.3 FEET (174.4 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH 

Superior

602.13183.53601.94183.47602.82183.74

1986

599.61

182.76

1926

601.54183.35

MichHuron

579.36

176.59

578.31

176.27581.63177.28

1986

576.57175.74

1964

578.97176.47

St.

Clair

574.87175.22574.57175.13576.87175.83

1986

572.24174.42

1934

574.54175.12

Erie

571.88

174.31572.01

174.35574.05174.97

1986

569.03173.44

1934

571.85

174.30

Ontario

245.44

74.81

246.52

75.14

248.46

75.73

1973

243.14

74.11

1935

246.10

75.01

MAY MEAN LAKE LEVELS

(IGLD 1985)

* 2015 Ft.

M.

2014 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional** Average, Maximum and Minimum for period 1918-2014

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

May 2015

The overall Great Lakes basin received above average precipitation for the first time in four months. The Lake 

Ontario basin was the only basin with below average precipitation at 91% below average. All other basins had 

above average precipitation, ranging from 13% to 18% above average. Lakes Superior and Erie received above 

average net basin supplies in May, while lakes Michigan-Huron and Ontario received below average supplies. The 

tables below list May precipitation and water supply information for all Great Lakes basins. 

A comparison of monthly mean lake levels for May to long-term average (1918-2014) shows Lakes Superior and 

Michigan-Huron to be 6 and 4 inches above long-term average, respectively. Lake St. Clair and Erie were 3 and 4 

inches, respectively, above their long-term May averages, while Lake Ontario was 7 inches below its May average. 

 

PRECIPITATION (INCHES) 

BASIN 

May 12-Month Comparison 

2015 Average Diff. % of 

Average 

Last 12 

Months 

Average Diff. % of 

(1900-2012) (1900-2012) Average 

Superior 3.25 2.76 0.49 118 32.21 30.43 1.78 106 

Michigan-Huron 3.57 3.03 0.54 118 32.92 32.48 0.44 101 

Erie 3.85 3.39 0.46 114 31.81 35.59 -3.78 89 

Ontario 2.83 3.11 -0.28 91 30.48 35.83 -5.35 85 

Great Lakes 3.42 3.03 0.39 113 32.19 32.68 -0.49 99 

 

 LAKE May Net Basin Supplies1

 (cfs) May Outflows2 (cfs) 

2015 Average 

(1900-2008) 2015 Average3(1900-2008)

Superior 200,000 182,000 85,000 75,000 

Michigan-Huron 246,000 251,000 201,000 189,000 

Erie 72,000 48,000 218,000 216,000 

Ontario 34,000 60,000 232,000 260,000 

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