One of the UK’s rarest fish is moving closer to returning to its historic breeding grounds in Powys after being cut off by weirs for 170 years.

The Unlocking The Severn project by the Canal & River Trust, Severn Rivers Trust, Environment Agency and Natural England is in the process of reopening 150 miles (241km) of the river for twaite shad by creating routes around four major weirs.

Two large fish passes alongside Victorian weirs at Diglis and Bevere, near Worcester, have been completed as part of the conservation project, the largest of its kind in Europe.

Historical records show the fish spawning as far up the river as Welshpool – and although the current work has not quite brought them into Powys yet, it could mean the fish return to Montgomeryshire next year.

Work on a particularly tricky weir at Stourport means the fish cannot reach as far as Shropshire just yet.

"We have historical records of twaite shad reaching as far as Welshpool," said Jennie Hermolle, communications and marketing officer at Unlocking the Severn.

"So far we have three of our four fish passes open to the river.

"Unfortunately the third site is still under construction until the autumn – it is the most challenging location as the only access for plant and material is via river barge so this site has been most severely impacted by higher river levels, and having the longest build-time as a result.

"So for the twaite shad to have the chance to get all the way to Powys it will be the 2022 shad run.

County Times: OVERHEAD: The completed work

"However we’re already seeing salmon using the passes, so it should help more Salmon reach higher upriver, more easily. So those benefits will be immediate."

The shad prefer to spawn in flowing water over gravel beds at night, in noisy “bull” events with lots of splashing as the male and female swim in a tight circle, as if chasing each other, as the eggs and milt, or semen, are released.

Although the events take place under cover of darkness, the distinctive sound can be recorded from the river bank to estimate the number of spawnings in different locations.

Good spawning conditions can result in a peak year for new shad, which can live for eight to 10 years and return to the river up to five times to spawn, so monitoring near Worcester as part of the project could give an early indication of the prospect for the population in coming years.

County Times: Embargoed to 0001 Friday May 7 Undated handout photo issued by the Canal & River Trust of a twaite shad as one of the UKÕs rarest fish is getting the chance to return to historic breeding grounds on the River Severn which have been cut off by

Jason Leach, programme director at the Canal & River Trust, said: “It’s never too late to give nature the chance to recover.

“And our project’s night-time riverside spawning vigils are a fitting way to begin recording the recovery of the fish affected so badly when our predecessors inadvertently caused a big problem for migratory fish by the building of the weirs such a long time ago.

“We hope lots of volunteers will be inspired to join us to witness and record the spring shad spawning phenomenon.”