Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2010

MAY

1973

JUN

1952

JUL

1947

AUG

1947

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2011

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

19731935

JUN

19521935

JUL

19471934

AUG

19471934

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

2012

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

2010

MAY

1986

JUN

1986

JUL

1986

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2011

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

2012

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

2010

MAY

1986

JUN

1986

JUL

1986

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2011

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

2012

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

600.39

183.00600.10

182.91

602.62183.68

1986

599.48182.72

1926

601.25

183.26

MichHuron

577.53176.03577.13

175.91

581.46

177.23

1986

576.15

175.61

1964

578.71

176.39

St.

Clair

574.11

174.99573.79174.89576.84175.82

1986

571.92174.32

1926

574.28175.04

Erie

571.88

174.31

571.52

174.20

574.08174.98

1985

568.83173.38

1934

571.59174.22

Ontario

245.80

74.92

245.57

74.85

248.20

75.65

1973

242.88

74.03

1935

245.67

74.88

APRIL MEAN LAKE LEVELS

(IGLD 1985)

* 2012 Ft.

M.

2011 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional** Average, Maximum and Minimum for period 1918-2010

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. Tables of possible storm-induced rises at key locations on the 

Great Lakes are available on request. The Corps also publishes the "Great Lakes, Connecting Channels and St. 

Lawrence River Water Levels and Depths,” weekly, which provides a forecast of depths in the connecting rivers 

between the Great Lakes and the International Section of the St. Lawrence River. This information is available on the 

internet at http://www.lre.usace.army.mil/glhh. 

Great Lakes Basin Hydrology

April 2012

The Superior basin experienced slightly above average precipitation in April, while the Michigan-Huron, Erie and Ontario 

basins all received below average precipitation last month. Over the past 12 months, Lakes Superior and MichiganHuron have received below average precipitation. Lake Erie has received above average precipitation over the past 12 

months and Lake Ontario has received near average precipitation. Precipitation over the entire Great Lakes basin was 

below average in April and slightly above average over the past 12 months. In April, the net supply of water was below 

average for all the Great Lakes. The tables below list April precipitation and water supply information for all Great Lakes 

basins. 

A comparison of monthly mean lake levels for April to long-term average (1918-2011) shows Lakes Superior and 

Michigan-Huron were 10 and 14 inches below average, respectively. Lake St. Clair was 2 inches below average in 

April, while Lakes Erie and Ontario were 4 and 2 inches, respectively, above average. Boaters should be aware of 

hazards to navigation due to continued below average water levels on the upper lakes. 

 

PRECIPITATION (INCHES) 

BASIN 

April 12-Month Comparison 

2012 Average Diff. % of 

Average 

Last 12 

months 

Average Diff. % of 

(1900-2008) (1900-2008) Average 

Superior 2.18 2.01 0.17 108 27.03 30.51 -3.48 89 

Michigan-Huron 1.84 2.60 -0.76 71 31.98 32.44 -0.46 99 

Erie 1.84 3.16 -1.32 58 45.30 35.40 9.90 128 

Ontario 2.12 2.91 -0.79 73 35.81 35.71 0.10 100 

Great Lakes 1.96 2.54 -0.58 77 32.96 32.64 0.32 101 

 

 LAKE April WATER SUPPLIES1

 (cfs) April OUTFLOW2 (cfs) 

2012 

Average3

(1900-2008) 2012 

Average3

(1900-2008)

Superior 85,000 150,000 55,000 68,000 

Michigan-Huron 87,000 284,000 170,000 182,000 

Erie 19,000 67,000 219,000 207,000 

Ontario 34,000 93,000 273,000 251,000 

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

1

 Negative water supply denotes evaporation from lake exceeded runoff from local basin. 

2

 Does not include diversions. 

3

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