A barrier arrangement for blocking a water passage or channel against the admission of a foreign or unfamiliar object, such as underwater vessels, frogmen and the like. The arrangement comprises a net (1) of considerable tensile strength intended to be stretched across the water passage. The bottom edge of the net (1) is anchored to the sea-bed and the net can be activated from a passive state, in which it may lie on the sea-bed, to an active barrier state. To this end, the upper edge of the net (1) is connected to an inflatable and deflatable lifting hose (3) which when evacuated is essentially flat and which when inflated is able to lift the upper edge of the net towards the surface of the water, so as to stretch the net between the sea-bed and the surface of the water. The invention also relates to a barrier net and to an anchoring means for use with the arrangement.