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FFI Siphon Fish Passes

FFI Siphon Fish passes


  • All-species fish passage
  • Huge cost savings on new builds
  • Easy maintenance
  • Low visual impact on the surrounding environment


The FFI Siphon Fish pass is a unique concept bringing two tried and tested systems together to provide the ultimate in fish passage in technology.

Traditionally, pool and traverse fish passes are used mainly by larger, more athletic species, however by incorporating this type of pass into a tubular siphon, the flow rate through the pass can be controlled, allowing targeting of smaller species. The FFI Siphon Fish pass can easily handle salmonid migration, but during off-season, can be slowed to allow small species, including even frogs and elvers to use the pass. As an optional extra, elver substrate can also be fitted inside the pass to aid eel passage.


The FFI Siphon Fish pass is manufactured using pre-fabricated lengths of Vinyl-Ester pipe, allowing it to be extremely robust, and easy to transport and install. The installation typically requires the excavation of a trench, allowing the pass to be laid prior to be backfilling, similar to the installation of a common pipeline. Usually there is no requirement for any foundation, with some installations requiring a period of days rather than weeks. Complicated concrete works can be avoided, meaning along with allowing a far wider variety of fish to use the pass, the build cost is often far lower.

As standard, the pass incorporates a number of viewing windows to allow inspection, and a set of sluice paddles in the base of each baffle, which can be opened in a single action to flush the siphon and clean debris. Other than occasional visual inspection and flushing, the pass requires very little attention, coupled with an exceptional life expectancy due to the high quality materials used.


Low impact on environment


As the siphon is essentially a pipe, the majority of the pass can be buried in the ground, with only the viewing windows requiring access. The design allows for routing the pass around obstructions, and also colouring to suit the surrounding environment.

The FFI Siphon Fish pass is controlled using a small vacuum pump, which “tops up” the vacuum in the siphon as water carrying air reduces the siphon effect. The vacuum pump operates automatically using a very small amount of power, often coupled with a small solar panel.


ACE also offer a range of fabricated fish and eel solutions for existing structures:

  • HDPE Larinier tiles, quick and easy to install
  • Fabricated Larinier Passes, custom built
  • Modular Eel passes
  • Special fabrications, including Alaskan “A” and Denile fish passes


For information on our recent fish pass installations, please see our case studies or contact us to discuss your requirements.



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