Inland lakes not between more than one state or capable of interstate commerce are regulated solely by the state they reside within. This is why you do not see the coast guard enforcing laws in any of these lakes. If it is a body of water that is capable of commerce between states now the coast guard has jurisdiction and requires a coast guard masters license to operate for hire. This includes interstate rivers, the Great Lakes, lake Champlain, Lake Tahoe just to name a few.
I know someone will claim to have seen the CG on their landlocked lake doing ice water rescue or something of that sort. Search and rescue is guided by very different laws and policies than law enforcement. Other agencies ask for our assistance and we can help them with SAR. But our licensing policies do not effect inland lakes. Your state may require the same license, but I know very little about state laws.