Ordinary High Water Mark (OHWM)

The ordinary high water mark (OHWM) is defined in the Part 325 administrative rules as follows:

(j) "Ordinary high water mark" means the elevations set by the act. When the soil, configuration of the surface, or vegetation has been altered by man's activity, the ordinary high water mark shall be located where it would have been if this alteration had not occurred

The OHWM is the elevation along the shoreline where a construction permit under Part 325 is required for such activities as dredging, seawalls, rock revetments, permanent docks and other structures. The elevations are listed in Section 32502 of Part 325. The elevations are referenced upon the baseline datum set called International Great Lakes Datum 1955 (IGLD 55).

These elevations have since been revised to a new datum set based upon studies conducted by the U.S. Army Corps of Engineers in the mid-1980s now called IGLD 1985. These revised elevations are shown here:

Revised Ordinary High Water Mark (OHWM) for Part 325 Great Lakes Submerged Lands
  1955 OHWM 1985 OHWM
Lake Erie 571.6' 572.2'
Lake St. Clair 574.7' 575.3'
Lake Michigan/Huron 579.8' 580.5'
Lake Superior 601.5' 602.6'