Real property rights vary by state. Here in WA, you can own some beach and, based on my very limited knowledge, there is some process to acquire tideland rights in order to, say, build a dock.
WA beach owernishp is to mean low tide. Not sure how socks work but I know in most places in the places in the Puget Sound won't let you build bulkheads out into the beach anymore to protect the environment.