This Note develops a simple set of principles useful for defining navigable waters in a contemporary context. Part I considers why federal admiralty jurisdiction exists, and traces the evolution of the phrase navigable waters as a term of art. Part II analyzes the conflicting contemporary definitions of navigable waters. Part III resolves the conflict by proposing guidelines that address the major concerns of all competing definitions. The system advocated is consistent with the goals of admiralty, constitutionally sound, easy to apply, and focuses attention on the nexus test to resolve the issue of whether particular cases belong in admiralty