From warm-water reefs in the Florida Keys to kelp forests off California and volcanic drop-offs in Hawaii, the United States offers a full-spectrum dive, freedive, and snorkel playground across two oceans, the Gulf of Mexico, and clear freshwater springs and alpine lakes. At country scale, the key is choosing the right coast and season: Florida delivers year-round reef and wreck diving with peak hurricane risk in late summer; Hawaii is steady and warm with winter north swells and humpback whales; California shines for kelp, sea lions, and macro when swell is low and visibility improves in late summer and fall; inland, Florida springs and Lake Tahoe provide cold, clear training and specialty dives. Strong infrastructure, broad flight access, and a mature dive industry make logistics easier than many destinations, but local rules vary by state, park, and sanctuary. Plan conservatively, respect marine life, and let conditions choose your exact sites.