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Mitigation banks are a form of regional compensatory mitigation, with the goal of providing greater resource protection and benefit to the public. Mitigation banking promotes the restoration of large wetlands to provide off-site compensation for multiple small mitigation projects, resulting in economies of scale in planning, implementation and management. Consolidation can result in wetlands of greater value because of their size and the commitment to long- term management. Mitigation banking can also result in wetlands of greater ecological value by reducing the effects of habitat fragmentation and through the restoration of historic wetland diversity and distribution within a watershed.

A mitigation bank site is a property purchased and developed by a public agency or utility to earn credits to compensate for adverse impacts to wetlands due to development activities of other agencies, utilities or, in specific instances, private sector developers. Credits are generated through the restoration, creation, and/or enhancement of wetlands.

King County's administrative rules on wetland mitigation banking were adopted in January of 1999. For an overview, please read the Executive Summary of wetland mitigation banking rules.