What On federally controlled waters which vessels are required to carry a whistle or horn or some other means to make an efficient sound signal?

On federally controlled waters, vessels such as recreational boats, commercial vessels, and certain larger vessels are required to carry a whistle, horn, or other means to produce an efficient sound signal. This requirement is outlined in the U.S. Code of Federal Regulations, specifically under Title 33, which governs navigation and navigable waters. The sound signaling devices are essential for safety, allowing vessels to communicate their presence, intentions, and maneuvers to others, especially in low visibility conditions.