A shut-off device for a pipe in a pipeline and responsive to ingress of water, has at least two valves for installation in the pipe of the pipeline. Each valve has a valve member supported for movement between an open position when the valve is open for passage of a fluid through the pipe, and a closed position when the valve is closed for preventing passage of the fluid through the valve. The device includes a buoyant member associated with the valve members for causing movement of the valve members to the closed positions upon ingress of water to the buoyant member. The valve members are moved to the closed positions in respective upstream and downstream directions of passage of the fluid through the pipe.