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Ordinary high water mark

Under Washington's Shoreline Management Act, the ordinary high water mark (OHWM) is defined as a biological vegetation mark. For locations where the OHWM cannot be found, our Shoreline Master Program guidelines include default elevation lines for tidal and fresh water shorelines. 

Definition

The ordinary high water mark 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."
In relation to extreme high and extreme low water, the position of the OHWM varies from site to site and changes through time due to a number of factors including:
Shoreline cross-section showing extreme high water mark, ordinary  high water mark, and extreme low water mark in relation to vegetation and distance from shore.

Ordinary high water mark in relationship to extreme high and extreme low water marks.

  • Accretion
  • Activities of beavers and other animals and organisms
  • Consistency of pool elevations
  • Erosion
  • Groundwater
  • Land-use changes
  • Presence of peat
  • Soils
  • Stormwater runoff
  • Substrates
  • Waves
  • Wind