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Identifying the Ordinary High Water Mark on Inland Lakes and Streams and the Great Lakes
PART 325: The OHWM for each Great Lake is an elevation set by Part 325 and is referenced upon the baseline datum set called International Great Lakes Datum 1985 (IGLD 85). See the EGLE Great Lakes OHWM website for information on Part 325 OHWM elevations. In addition, the US Army Corps of Engineers (USACE) has jurisdiction over these areas and also has OHWM elevations; see USACE website for more accurate daily information on Great Lakes Water Level Data. When looking up daily data, use the Daily Lakewide Average Water Levels tables to select the closest date elevation. If you are using the IGLD 85 datum as the OHWM reference, this is the elevation you enter on the Joint Permit Application for Great Lakes Observed Water Elevation. You may also use a relative reference that is based on measurements in relation to a benchmark or point location identified in the field (such as a water level or base of a tree). The OHWM elevation can be converted based on this onsite observed data. See example drawings.
Part 301: OHWM for inland lakes is the line between upland and bottomland identified by the presence of a distinct change in character of the land caused by successive changes in water levels. This line is identified in the field based on observed physical characteristics and may be reported by referencing either land survey elevation information or a relative benchmark such as observed water level or the base of a tree. A surveyed elevation is typically referenced to the National Geodetic Vertical Datum (NGVD 29 or NAVD 88). If the actual land elevation is not known (i.e., no land survey is done), then use a relative reference elevation such as 0 for an observed water level or a static benchmark. The OHWM elevation to report on the JPA will be the vertical distance from that benchmark to the physical line observed in the field. If using a water level as the benchmark, report the date of observation. The OHWM is used for calculating impacts from the proposed activities so the actual surveyed elevation itself is not necessary in many cases. The necessary information is where the OHWM lies vertically and horizontally in relation to the existing and proposed features on site (e.g., water levels, bottom of stream, dock dimensions, etc.). See EGLE’s YouTube Series for OHWM video tutorials, and the sample OHWM drawings for more information. Some inland lakes have a legally established OHWM elevation (Legal Lake Level). For information, see EGLE’s YouTube video describing Legal Lake Levels. Contact your County Drain Commissioner for established Legal Lake Levels in your area.