Irrigation-influenced wetlands

Large areas of eastern Washington have been converted to agriculture and are irrigated. Some agricultural areas in western Washington are also irrigated. Many wetlands have formed adjacent to irrigation conveyance systems and in low-lying areas where irrigation occurs.

Regulating wetlands in irrigation areas

Our authority to regulate wetlands is based in two principal statutes:

Both laws define “wetlands” and “artificial” wetlands, such as irrigation ditches and canals. The definition in both laws states that an “artificial” wetland must be both “intentionally created” and created in an upland area.

A wetland that may be influenced by irrigation is considered a wetland under the state definition and regulated accordingly. However, this does not mean that irrigation-influenced wetlands cannot be filled; it means that one must obtain state approval to do so.

Distinguishing wetlands and artificial wetlands

It is often difficult to differentiate between wetlands and artificial wetlands in the field. This is because it's difficult to determine whether the wetland was created intentionally and whether it occurred in an upland or in an already existing wetland.

It can be particularly difficult to make these distinctions because it's hard to determine the relative influence of natural water sources like precipitation, snow melt and groundwater as opposed to regional and site-specific irrigation practices.

How we regulate irrigation-influenced wetlands

Our focus sheet on irrigation-influenced wetlands explains how we address a wide range of situations where wetlands are influenced by human activities. The focus sheet does not address federal or local laws. Consult with the U.S. Army Corps of Engineers to understand if federal laws apply to you. Contact your local city/town or county planning department for local laws.

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