UK’s first FFI Siphon Fish Pass installed at Wissington

The Siphon Fish Ladder is an innovative fishway from the Netherlands, which can be applied to facilitate fish passage at any watercourse obstruction and structures including weirs, penstocks and  flap valves. The Siphon fish ladder allows passage of most types of fish including eels and even frogs and tadpoles have been observed using the system.

A Siphon Fish Ladder is, in essence, a pool and weir fish pass contained within a siphon. This offers benefits as the flow rate is not subject to that of the watercourse, but can be fully adjusted and changed by alternating the size of an air bubble within the siphon using a vacuum pump. Siphons Fish Ladders are already a much tested concept in the Netherlands, where nine are currently  operational with test results confirming the effectiveness of the concept for fish species found in Dutch inland waters.

The UK, however, poses new challenges for the Siphon Fish Ladder. In the Netherlands, salmon and trout have not been present in the waters where fish siphons are installed. The criteria for a fish siphon have therefore been changed for the UK and the design has been adapted to allow passage for these species. Specialists from the Environment Agency have been involved in fine tuning the design and the Siphon. A study was carried out over a 6 week period in 2011, using catch and release methods. A total of 13 species, over 887 total fish were observed, including European Bitterling, common Bream, Pike, Perch and European Eel.

The siphon’s versatility allows accurate control, making the user able to tailor the flow to the local species, and also allows a much larger range of species to use the pass.