Cuddington Fish Pass

A section of river on a historic mill leat, which was previously impassable to fish, was restored through the construction of a rock ramp fish pass and habitat improvement work.

Project Highlights

A historic barrier to fish is now passable during all flow conditions
400 metres of river habitat improved for fish, invertebrates and plants
3 cattle drinks installed to prevent damage to river bank from livestock

Cuddington Mill, as is typical with most mills, had a weir associated with it that was a barrier to fish movement.

Fish need to be able to move between habitats to spawn, fed and find new habitat. Fish passage is therefore important for the resilience of populations of all fish species in the River Thame. In 2019, RTCT remedied this fish passage issue with the installation of a rock ramp structure.

History of the fish passage issue

Old crumbling weir structure in the 1990s
which became a rock ramp weir in 1997
and prior to works in 2019 after trees cut back showing degraded impassable structure

Designing the fish pass required surveying, flow monitoring and level gauging.

Data was gather to determine the physical parameters required in the design to make the pass passable to all fish sizes and species at all flows and in particular low flows.

The solution was to create a rock ramp comprising lines of boulders, each with a notch, which form pools between.

The pools step down in small, manageable drops and the notches are placed to allow flow even during low river levels. All of the dimensions and levels were set to ensure all fish species and life stages of fish could swim up and downstream at all times of year. Large boulders were added to each pool to dissipate the force of the flows, ensuring smaller species with lesser swimming ability can still pass.

The project included habitat improvement work along 400 metres of river.

Branches were selectively removed from trees to let in light to the river and banks and to create brash material to be used in the river as berms. The berms created scruffy marginal habitat features that reduced the width of the river and vary both flow speed and direction providing different niches for a variety of fish, invertebrates and plants. The brash itself provides good cover for fish from predators and increases the fish holding capacity of the stretch.

The final part of the project included creation of 3 cattle drinks.

Cattle poaching had destabilised some areas of bank and was creating significant sediment input in places. The cattle drinks were created in areas favoured by the cattle by grading back a section of bank, addition of gabion stone topped with gravel to create a firmer base. This was followed by some limited fencing to funnel the cattle to the feature and limit encroachment into the river.

Special thanks to…

Our funders, The European Agricultural Fund for Rural Development

Our partners, the Environment Agency,

including the local EA officers for their support throughout the project

Our contractors, Amenity Water Management

The landowners, A+M Spencer Bernard Trust, for permission to carry out the works

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