The water within natural inland lakes is held in the public trust. However, property owners here have an ownership stake in the land under the water and can build docks or other structures anchored to the bottom of these lakes. This concept is known as Riparian Rights, and these rights extend to the center of the lake.
Riparian Rights entitle owners to build structures, and ensure that if lake levels recede, lakefront owners will still own all of the land outside of the water. They also can be used to prevent swimmers from trespassing, if the swimmer is standing on the bottom of the lake.
However, Riparian Rights owners cannot stop anyone from using the water itself, even if there is no public access point to the lake.
Within human-made lakes such as impoundments or former quarries, Riparian Rights do not apply. The bottomland of the lake may be entirely owned by a private entity (different than the individual shoreline owners) or by a public entity. Some impoundments are regulated by the Federal Government, further complicating the situation.
Property owners on human-made lakes have defined property boundaries, which are usually designed to extend a certain distance into the water. However, if water levels recede, property owners can find themselves with a strip of land that they do not own between their property and the water.