The proposed Adjustable Hydraulic Structure (AHS) is a uniquely designed barrier that could replace the Sixth Street Dam as the primary sea lamprey barrier on the river. The AHS structure has been proposed to be constructed approximately one mile upstream of the Sixth Street Dam. Sea lamprey escapement, upstream of the project site, would have a significant impact on the Lake Michigan fishery. The AHS is designed to ensure sea lampreys do not migrate upstream of the City of Grand Rapids. This structure would deny sea lampreys access to more than 1,900 miles of stream habitat, which would otherwise cost the Great Lakes Fishery Commission between $1.2 million and $1.8 million annually to treat with lampricides. An effective lamprey barrier structure on the Grand River is critical given that just one sea lamprey escapement event upstream of Grand Rapids could inflict millions of dollars in economic loss. The AHS is one alternative being evaluated for feasibility through the Environmental Impact Statement process being led by the Great Lakes Fishery Commission.