NOVELTY - The device (100) comprises a buoyant base member (110) removably coupled to a water-filled anchor member (210), and a locking member to lock the base member to the anchor member. The base member has a square, hexagonal or triangular shape and a dome shape to properly orient itself within the water, forms a tiling pattern without gaps over the body of water, absorbs solar energy, and transfers heat to the body of water. The anchor member comprises a first port located in a lower portion of the anchor member, and a second port located in the upper portion of the anchor member.    USE - The device is useful for heating a body of water, for blocking light and transmitting radiant heat to a body of water (claimed), in a natural setting such as pond or lake, and in man-made water containing apparatus such as pool or water-treatment lagoon.    ADVANTAGE - The device is easy to remove and store water in the pool, and is capable of economically heating the pools, ponds and other bodies of water thus providing a comfortable water temperature for swimming, preventing or slowing the formation of ice on the water's surface and promoting the growth of beneficial microorganisms in wastewater treatment lagoons or ponds.    DETAILED DESCRIPTION - The device (100) comprises a buoyant base member (110) removably coupled to a water-filled anchor member (210), and a locking member to lock the base member to the anchor member. The base member has a square, hexagonal or triangular shape and a dome shape to properly orient itself within the water, forms a tiling pattern without gaps over the body of water, absorbs solar energy, and transfers heat to the body of water. The anchor member comprises a first port located in a lower portion of the anchor member, and a second port located in the upper portion of the anchor member. A water flows into the first port and air exits the second port, where the rate of flow of air is dependent upon the diameter of each of the first port and second port. The base member and anchor member are made of a high density waterproof plastic resin. INDEPENDENT CLAIMS are included for:    (1) a method of heating a body of water; and    (2) a method of blocking light and transmitting radiant heat to a body of water.    DESCRIPTION OF DRAWING(S) - The diagram shows a front view of a buoyant water heating device.    Heating device (100)    Base member (110)    Bottom surface (130)    Top surface (140)    Anchor member (210)    Center section (320)    Bottom section. (330)