Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2016

NOV

1945

DEC

1945

2017

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

2017

JUN

2017

JUL

2017

AUG

1947

SEP

1947

OCT

1945

NOV

19451934

DEC

19451934

2018

JAN

1946

1935

FEB

1952

1936

MAR

19521935

APR

19731935

MAY

20171935

JUN

20171935

JUL

20171934

AUG

19471934

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

2019

JAN

1946

1935

FEB

1952

1936

MAR

19521935

APR

19731935

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

2016

NOV

1986

DEC

1986

2017

JAN

1987

FEB

1987

MAR

1986

APR

1985

MAY

1986

JUN

1986

JUL

1986

AUG

1986

SEP

1986

OCT

1986

NOV

1986

1934

DEC

1986

1934

2018

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

DEC

1986

1934

2019

JAN

19871935

FEB

1987

1936

MAR

1986

1934

APR

1985

CHART DATUM 569.2 FEET (173.5 METERS) 1934

Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2016

NOV

1986

DEC

1986

2017

JAN

1986

FEB

1986

MAR

1986

APR

1986

MAY

1986

JUN

1986

JUL

1986

AUG

1986

SEP

1986

OCT

1986

NOV

1986

1934

DEC

1986

1964

2018

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

DEC

1986

1964

2019

JAN

19861936

FEB

19861926

MAR

1986

1934

APR

19861926 CHART DATUM 572.3 FEET (174.4 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH 

Superior

602.92183.77603.05

183.81

603.38

183.91

1985

600.72

183.10

1925

602.07

183.51

MichHuron

580.38

176.90

580.28176.87582.35

177.50

1986

576.44

175.70

1964

578.87176.44

St.

Clair

575.85175.52

575.66175.46

577.30

175.96

1986

571.75174.27

1934

574.15

175.00

Erie

572.74174.57572.47174.49573.95174.94

1986

568.57

173.30

1934

571.10

174.07

Ontario

244.82

74.62

245.60

74.86

246.78

75.22

1945

242.19

73.82

1934

244.78

74.61

OCTOBER MEAN LAKE LEVELS

(IGLD 1985)

* 2018 Ft.

M.

2017 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional** Average, Maximum and Minimum for period 1918-2017

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 and Climate Change 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

October 2018

According to preliminary estimates, precipitation throughout the Great Lakes basin was above average in October.

Lake Superior and Lake Michigan-Huron received over 4 inches of precipitation and were above average by 48% 

and 54%, respectively, which led to above average water supplies. Lake Erie received 116% of average precipitation 

for the month and Lake Ontario received 108% of average precipitation. Despite slightly above average precipitation 

for Lakes Erie and Ontario, water supplies were below average for Lake Erie and near average for Lake Ontario. 

Outflows from all the lakes continued to be above average during the month of October. 

October monthly mean water levels were above their long-term average for all lakes. From September to October, 

all the lakes declined, except for Lake Superior. Typically, Lake Superior begins its seasonal decline in October, but 

the wet conditions led to a rise of 3 inches in the last month. Lake Michigan-Huron declined by 2 inches from 

September to October, while Lakes St. Clair, Erie, and Ontario fell by 4 inches. Lake Superior’s monthly mean level

for October was 2 inches below last year’s level and Lake Ontario was 9 inches below its level from a year ago. 

Lakes Michigan-Huron, St. Clair, and Erie October levels were above last year’s levels by 1, 2, and 3 inches, 

respectively. 

PRELIMINARY PRECIPITATION (INCHES)

BASIN

October 12-Month Comparison

2018 Average Diff. % of 

Average

Average Last 

12 Months

Average Diff. % of 

(1900-2016) (1900-2016) Average

Superior 4.26 2.88 1.38 148 28.48 30.58 -2.10 93

Michigan-Huron 4.53 2.94 1.59 154 30.56 32.55 -1.99 94

Erie 3.29 2.83 0.46 116 35.67 35.62 0.05 100

Ontario 3.42 3.17 0.25 108 33.11 35.87 -2.76 92

Great Lakes 4.13 2.93 1.20 141 30.84 32.77 -1.93 94

 LAKE

October WATER SUPPLIES1 (cfs) October OUTFLOW2 (cfs)

2018

Average

(1900-2008) 2018

Average3

(1900-2008)

Superior 178,000 40,000 95,000 80,000

Michigan-Huron 98,000 1,000 221,000 191,000

Erie -41,000 -21,000 237,000 201,000

Ontario 8,000 7,000 272,000 243,000

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