In order to allow migratory salmon and sea trout to negotiate the barrage, a fish pass with fish counter and viewing area was installed next to the north bank pavilion.

The design required non-return valves to operate on the fish passage so that the impact of tidal water on the fresh water on the upstream river and artificial whitewater course could be minimised. This would allow fish to swim downstream and out to sea, but prevent sea water from flowing upriver through the passage during high tide.

The National Rivers Authority (NRA) was understandably concerned about the impact of these valves on the fish and as part of the design it was proposed to use duckbill check valves to address these concerns. It was considered that the flexible rubber design would reduce the risk of damage to the fish.