In the Dutch part of the Rhine many hydraulic works (sluices, barrages, etc.) are situated which are considered to be barriers for upstream fish migration. Because of intensive shipping these works are always combined with big shipping locks. Until recently no data were available concerning fish migration via these locks. This was studied in the river Lek at the Hagestein barrage.
Due to the short length of the study period and few recaptured salmonids (salmon, sea trout, rainbow trout) no conclusive evidence about the effects of the shipping lock on salmonid migration was obtained. However, the results do suggest that the Hagestein barrage complex forms a serious barrier for upstream migration of salmonids. Several other fish species on the other hand were observed to migrate through the lock. Therefore, depending on target species and management goals, the presence of shipping locks should be taken into account when considering improving fish migration possibilities.