Fisheries Fish Passage

Fish Passage

Water control structures such as weirs, mill structures, locks and sluices can present impassable barriers to fish, which restrict migration and prevent access to valuable spawning grounds and nursery habitat. These structures can also compartmentalise fish populations and prevent interaction between them. Abstractions and outfalls can also pose a threat to fish populations through entrainment and impingement, if they are left unscreened, or if existing screens are not suitable.

Providing free and unhindered fish passage is a major objective of the EU Water Framework Directive (WFD) in achieving good ecological status. It is also important in the context of the EU Eel Regulations which gives the Environment Agency additional powers to require screening of abstraction intakes and outfalls. Ensuring free fish passage and providing adequate screening can also have other social and economic benefits.

There are a number of ways in which fish passage can be provided, depending on the size or nature of the barrier, and the type of fish for which an improvement is to be designed. Structures ranging from formal fish passes through to nature-like bypass channels or easements can be designed and created to offer options for passage for coarse fish, salmonid species, eels and lamprey.

OHES is able to offer feasibility studies and assessments of barriers to determine the best option for providing fish passage in a range of situations. We are then able to provide detailed design options and reports, and project management of the construction phase. Whether you need a formal engineered structure or a natural fish pass option, we will be able to help. We can also provide technical input to research and policy development on fish passage issues.

Additionally, we provide tailored monitoring programmes and investigations to measure entrainment and impingement impacts and screening efficacy; as well as reference monitoring and fish population surveys in freshwater, estuarine and marine environments. Contact us for further information.


Case Studies

Fish Pass and Nature-Like Bypass Channel Design and Installation and at Newbridge Mill on the River Windrush

OHES has recently completed a project on the River Windrush, close to its confluence with the River Thames.

The weir systems at Newbridge Mill were historically impassable to fish, and a solution was required by the Environment Agency in order to open up free fish passage over 5km of habitat in the River Windrush to fish from the River Thames.

A derelict channel was chosen as a suitable pathway to create a natural fish bypass channel, which in itself would create over 100m of new stream habitat, suitable for spawning and nursery habitat.

A formal fish pass was constructed at the upper end of the channel, which would enable coarse fish and salmonid fish to access the River Windrush upstream, while a new channel was excavated at the lower end of the channel to form the entrance to the bypass channel.

This was designed to provide a suitable attraction flow which would encourage fish to use the new bypass. The project is complete, and the channel has quickly developed from a stagnant ditch into a fast flowing stream with a clean gravel bed. The fish pass was also designed to allow for monitoring equipment to be installed onto the fish pass to assess the use of the channel.


Wicksteed Park – Design of passable control structures.

As part of a major Heritage Lottery Funded restoration plan for the lake and River Ise corridor at Wicksteed Park in Kettering, we provided a series of designs for replacement water control structures at the intake and outfall of the lake which would provide free passage for coarse fish and eels.



Kinnairdie Link Road – Review of Fish Pass Designs

On behalf of the Highland Council, OHES was commissioned to review engineering drawings for a proposed water control structure associated with the Kinnairdie Link Road development. We are working with the Highland Council and their appointed engineers (URS) to develop designs which provide free passage for coarse fish, salmonid species, eels and lamprey.