Cover device and blanket for covering liquid surfaces

Cover device for covering a surface of a liquid in a pond, having a shell (2) defining an inner cavity, and the inner cavity is to be filled at least partly with liquid, wherein the inner cavity is divided in at least two chambers (3,4) by a separating means (5,51,52), and one of the chambers (4) is provided by at least one opening (6) formed in the shell (2), and a weight member (8) is arranged in the proximity of said opening (6), characterized in that said weight member (8) is provided with a through hole (8a), and arranged in the opening (6) of said shell (2).

A composite blanket formed on the surface of a storage reservoir containing liquid, characterized by consisting of several cover devices (1,11) according to any of preceding claims arranged in at least one layer.