Fundamentally Improving Salmon Habitat Act or the FISH Act - Amends the Water Resources Development Act of 2000 to revise requirements for studies and ecosystem restoration projects for the lower Columbia River and Tillamook Bay estuaries, Oregon and Washington. Directs the Secretary of the Interior to: (1) conduct studies and ecosystem restoration projects with total costs of $2 million or greater per project (designated as "large projects"); and (2) provide grants to the Lower Columbia Estuary Partnership, the Lower Columbia Fish Recovery Board, and the Tillamook Estuaries Partnership to conduct projects with total costs of less than $2 million per project ("small projects"). Revises and adds requirements relating to administration of such projects, including the provision of technical assistance to entities carrying out small projects, the determination of priority for large and small projects, and the allocation of funding for small projects.