Helping Wild Fish at Hurstbourne Priors

Chub ©  Jack Perks

Historic structures are important to our chalk stream heritage, but can pose a problem for migrating fish. At Hurstbourne Priors, the Watercress and Winterbournes partners have been getting our freshwater friends on the move.

Around one mile outside the village of Hurstbourne Priors, the Bourne Rivulet winds a tree‐lined path across the countryside. Like many in our region, this chalk stream has been changed by years of people living and working along its banks, sometimes to the detriment of its resident wildlife.

Chalk stream fish tend to be keen travellers, since they often need different environments for feeding, breeding, and growing to adulthood. Barriers which cut off access to these spaces can result in smaller fish populations that are vulnerable to threats like disease, pollution, and habitat loss.

On this stretch of stream there was a barrier in the form of an inactive sawmill, where the stream was historically altered to power a water wheel. While it's a valuable heritage feature, the mill separated fish in the upstream breeding areas from those in the adult habitat downstream.

The landowner was keen to address this issue in a way that retained the heritage value of the site, and Watercress and Winterbournes offered a solution. In November 2020, scheme partner Wessex Rivers Trust transformed the mill from a barrier to a bridge, giving local fish access to over 3km of chalk stream habitat.

Rock ramp

This stretch of stream is retained in a mill pond before passing through the site via several concrete channels. Of these the overspill channel is the most welcoming for migrating fish, however multiple weirs made it largely impassable; the steps were too high for smaller species, and the water too low for larger ones.

We cut away sections of the weir steps, then added rocks and gravel in a winding pattern. This gentle, sloping ramp now mimics a natural stream bed, with deeper pools for resting and nooks where smaller animals can hide. Its meandering shape will also encourage a lively flow to attract fish and help sweep away debris.

Sluice repairs

One of the mill's key heritage features is its pond, the water level of which is maintained by a complex sluice system. Several wooden boarded hatches can be raised or lowered to alter how much water enters and exits the pond through each channel. As these degraded over time, however, their operation was affected.

We replaced the old wooden boards with new ones, allowing the landowner full control over water levels around the mill. These repairs will allow the pond to better reserve water, which can then be released to keep the rock ramp usable and debris-free in times of lower stream flow.

Weir notching

Further downstream, where the concrete overspill channel ends, there was one last hurdle to cross. Another weir forms a boundary between the enclosed channels of the mill and the more natural watercourse beyond. Its flat concrete sill presented another barrier for small fish, especially when the stream's water was low.

We cut a trapezoid-shaped notch into this weir, which will not only improve accessibility but also speed up the flow of water through this point. This will help attract fish into the overspill channel, where they can climb the rock ramp and travel onwards upstream.

Weir on the Bourne Rivulet at Hurstbourne Priors © Wessex Rivers Trust

The Bourne Rivulet between Hurstbourne Priors and St Mary Bourne; weir on the overspill channel at the site of a disused saw mill © Wessex Rivers Trust

Cherishing our chalk streams

We're delighted to have been able to make these improvements - huge thanks to the landowner for their support and to Wessex Rivers Trust for leading on the works. The two will be in contact this year to make any minor adjustments needed and implement a management plan for the site.

Watercress and Winterbournes is improving many habitats across the chalk streams that feed the Rivers Test and Itchen. We're also offering a range of activities to protect, enhance, and celebrate these special habitats and their local communities - why not explore the scheme?