The main purpose of this legislation, known as the "Defending our Dams Act," is to protect the Lower Snake River dams from any federal funding that would support their breach, alteration, or removal. The bill aims to ensure that these dams remain intact and continue to serve their functions, which include power generation, flood control, and navigation. Key provisions of the Act include a strict prohibition on the use of federal funds for any activities that would lead to the breach or functional alteration of the Lower Snake River dams.