Water levels for the previous year and the current year to date are shown as a solid line on the hydrographs. A projection for the next six months is given as a dashed line. This projection is based on the present condition of the lake basin and anticipated future weather. The shaded area shows a range of possible levels over the next six months dependent upon weather variations. Current and projected levels (solid and dashed lines) can be compared with the 1919-2012 average levels (dotted line) and extreme levels (shown as bars with their year of occurrences). The legend further identifies the information on the hydrographs.
The levels on the hydrographs are shown in both 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.
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 provided monthly as a public service. 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 Monthly Bulletin of the lake levels for the Great Lakes may be obtained free of charge by writing to the address shown in the contact section of this page or by calling (313) 226-6442, or send an email to email@example.com. Notices of change of address should include the name of the publication. This information is available on the internet at www.lre.usace.army.mil/Missions/GreatLakesInformation.aspx.