To provide an obstruction device having a flexible barrier element for rocks, suspended solids, and drifting articles, vertically installable between river banks in the direction perpendicular to a flowing direction, and used for all waterways and small rivers, in particular for torrents and similar river beds.

A catchment net 4 is attached between a lower supporting rope 5 and an upper supporting rope 6. The supporting ropes 5, 6 are anchored to the river banks 2, 3 by rope anchors 8, 9 attached to their ends, respectively. The rope anchor 9 of the upper supporting rope 6 is so attached as to be displaced from the rope anchor 8 of the lower supporting rope 5 in the flowing direction. Therefore, when the barrier is filled, the catchment net 4 is deformed by itself, and the water overflowing from the net, the rock, and drifting articles are not at all brought into contact with the net, or slightly brought into contact therewith even if they are brought in contact. In this way it is safely and permanently protected against the corrosion and abrasion effect of the overflowing water.