Check local rules, but public islands usually allow it.

It depends entirely on which islands you mean. Public beaches and national park islands (like the Channel Islands or state parks) generally permit launching kayaks and small boats from the shore, but there are often restrictions: designated launch areas, no motorized vessels in certain zones, or seasonal closures for wildlife. Private islands are a different story — you’ll need permission or a launch permit. The safest move is to look up the specific island’s land management agency (National Park Service, state parks, local government) and check their boating regulations. Most will have a simple PDF or map showing where you can and can’t launch. If you’re just talking about a random uninhabited island in a lake or river, you’re probably fine as long as it isn’t a wildlife refuge.

Just don’t assume “it’s an island” means “no rules.” That’s how you end up with a fine.