Aquatic Control Engineering

01777 249080

Siphon Fish Pass

The Siphon Fish Pass is an innovative fishway which can be applied to facilitate fish passage at any watercourse obstruction or structure including weirs, penstocks and flap valves. The Siphon Fish Pass allows passage of most types of fish, including small coarse fish and eels. 

A Siphon Fish Pass is a pool and weir fish pass contained within a pipe, which acts on the siphon principle.  Connecting two watercourses or the head and tail end of the same watercourse, the flow rate is not subject to that of the watercourse but can be adjusted and changed.  The adjustment is made simply by alternating the size of an air bubble within the siphon using a vacuum pump.  


Unique Design and Operation Features

  • The pipe design allows for the siphon to be installed underneath flood plains allowing existing flood defence standards to remain
  • The Fish Siphon Pass can be isolated at either end if necessary
  • Operation is successful even in very low flows increasing its use throughout the year
  • The Siphon shape allows for gauging
  • Built with sustainability in mind the siphon boasts low energy and water consumption requirements and solar powered options
  • Adjustable flow rates
  • Low maintenance requirements and flushing mechanisms built into the design


Research and Testing 

Siphon Fish Passes have been monitored and reported against (R. Beentjes 2012, Koopman 2011) in the Netherlands, where nine are currently operational.  The available studies both indicate clearly the ability for the Fish Siphon Pass to provide adequate passage to a range of small coarse fish and eel, in percentiles similar to that of the surrounding watercourses. 

Further monitoring by the Environment Agency is underway at one of our sites in the UK  Project Specific  Each Fish Siphon Pass is constructed specific to the needs of each project, taking into account fish species and local topography to determine the best solution. 

ACE installed the first Fish Siphon in the UK on the river Wissey in Norfolk during April 2012 and launched the technology wit an event in September 2012.  For more information you could see our Project Profile or Event Information Page