For the first time in 180 years an endangered and rare fish has reached an ancient spawning ground. The BBC has reported that DNA tests from samples have shown that the twaite shad, a type of herring, is present in the River Severn.

The discovery was made by the Worcestershire project, Unlocking the Severn, that has enabled the fish to return. Four fish passes have been created in the river to also provide safe passage for other migrating fish.

Charles Crundwell, from the Environment Agency, said it was “thrilling” to know the passages working. “Shad are rediscovering key habitat lost to them for so long – 35 generations for these fish,” he said. (photo:  Canal & River Trust/PA)

The fish were monitored using cameras filming through a unique underwater window, fish fitted with tiny tags, environmental DNA analysis of water samples, and volunteer citizen scientists taking water samples.

Unlocking the Severn is run by the Canal and River Trust in partnership with Severn Rivers Trust, Environment Agency and Natural England.

Lincomb Weir, Stourport-on-Severn is the fourth and final fish pass in the project

Lorna Pedersen, from the trust, said: “This year, from 100 tagged fish, shad were recorded travelling as far upstream as the final fish pass at Lincomb Weir, Stourport-on-Severn. “This proved shad were making use of the first three fish passes – great news for their first migration through new habitat.”

There are also fish passes at the Diglis Weir, Bevere Weir and Holt Weir all in Worcester. A full report on the environmental DNA analysis of water samples is due to be published by Natural England later this year.

Shad are a type of herring that migrate from the sea into freshwater every year to spawn. The silver fish use only four British rivers to spawn and historically the Severn was the most important, with hundreds of thousands of fish swimming up the Severn on their annual migration to their spawning grounds in the upper reaches of the river.

Their route was blocked in the 1840s by the building of large weirs for navigation – a common obstacle for migratory fish, with only 1% of rivers in England, Scotland and Wales free of artificial barriers, the Guardian reports. On average, there is at least one artificial barrier every 1.5km of river in Britain.