The present application discloses a retention device for retaining an item in a body of water, for example a swimming pool. In some embodiments, the retention device comprises at least one water-fillable receptacle connected to a retention element—for example a strap—that is placed over the item that is to be retained. When an upward force is applied to the retention element in a direction generally away from the surface of the body of water, the filled water receptacle restricts upward movement of the attached retention element, thereby maintaining the item in the body of water.