What is the federal government's role in determining whether a body of water is navigable for purposes of title?

Under the "equal footing doctrine," the federal government holds title to the beds of navigable waterways "in trust for future States, to be granted to such States when they enter the Union and assume sovereignty on an 'equal footing' with the established States." Montana v. United States, 450 U.S. 544, 551, 101 S.Ct. 1245, 1251, 67 L.Ed.2d 493 (1981). ³ Whether a particular body of water is navigable for purposes of title is a question of federal law. Utah v. United States, 403 U.S. 9, 10, 91 S.Ct. 1775, 1776, 29 L.Ed.2d 279 (1971).