A covering system that includes a first membrane, a first flotation member coupled to the first membrane. The first flotation member includes a first float and a first float compartment membrane, and the first float compartment membrane is coupled to the first membrane. The covering system also includes a first plurality of gas-relief passageways positioned either within the first float compartment membrane, or within the first membrane and adjacent to the first flotation member. And at least one of the gas-relief passageways within the first plurality is structured so that gas flows unobstructed through it when the system is used. Gas-relief openings formed between overlapping membranes may also be utilized as avenues through which gas may escape to atmosphere from beneath the covers and covering systems. Venting methods are also disclosed. The covering systems and methods may be applied to control odor, algae growth, and heat loss associated with the retaining various liquids, while permitting for the controlled release of gases that are produced.