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Shoreline Management

Ordinary high water mark

The ordinary high water mark (OHWM) as defined in the Shoreline Management Act (SMA) is a biological vegetation mark. Ecology's rules include a default tidal or fresh water elevation line for locations where the OHWM cannot be found.


The OHWM is defined as:

  • "that mark that will be found by examining the bed and banks and ascertaining where the presence and action of waters are so common and usual, and so long continued in all ordinary years, as to mark upon the soil a character distinct from that of the abutting upland, in respect to vegetation as that condition exists on June 1, 1971, as it may naturally change thereafter, or at it may change thereafter in accordance with permits issued by a local government or the Department of Ecology:
  • Provided, that in any area where the ordinary high water mark cannot be found, the ordinary high water mark adjoining salt water shall be the line of mean higher high tide and the ordinary high water mark adjoining fresh water shall be the line of mean high water."

The position of the OHWM in relation to extreme high and extreme low water varies from site to site.

At any given site, the OHWM will vary over time and according to factors that include wind, waves, erosion, accretion, soils, substrates, vegetation, land use changes, runoff, groundwater, the presence of peat, the constancy of pool elevations, and the activities of beavers and other organisms.

For more information

Law: RCW 90.58.030(2)(b) (Definitions)
Rule: WAC 173-22-030(11)

Determining the Ordinary High Water Mark on Streams in Washington State - DRAFT (Ecology Publication #08-06-001)

For assistance with ordinary high water mark determinations, contact Ecology's regional planner assigned to your town, city or county.

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