Salmon as far away as Scotland and northern France are making the River Mersey their new home.

In a week where the River Mersey has been named in the Top Ten most improved rivers in the country, the Environment Agency is carrying out research to see how far Salmon are travelling around the River Mersey, which was once called the most polluted river in Europe.

Salmon as far away as Scotland and northern France are making this river their new home, making it the first example in the UK and only a handfull in Europe of a former industrial river being naturally recolonised by salmon.

The Environment Agency has worked in partnership with Exeter University and through genetic research have established the origins of these salmon which started returning in 1999, the first time they had been seen in the river for over 60 years.

Sam Billington, Environment Agency Project Officer, explained: “Salmon are renowned for returning to the river where they were born to breed (spawn). When salmon came back to the Mersey we initially though they were from nearby rivers, such as the Ribble or the Dee, but this genetic research has shown that they majority are coming from much further away. Currently we have been able to pin point 36 rivers.

“We can’t say why the these salmon are choosing to make the Mersey their new home. But, what we can say is that their presence confirms that our rivers are the healthiest they’ve been for over 60 years allowing our native wildlife to flourish for the first time since the industrial revolution.”

Throughout September the Environment Agency will be carrying out its annual trapping, tagging and taking scale samples for genetic analysis of the Mersey Salmon. For the first time those interested will be able to keep up to date by following Sam Billington on Twitter (@SamBillingtonEA).

These tags allow for the salmons’ journeys up the River Mersey, passing through Manchester Ship Canal and into its tributaries to their spawing grounds to be monitored and analysed. This information allows the Environment Agency to better target its own and others’ environmental improvement projects, such as removing redundant weirs, for the benefit of people and wildlife.

Thirty years ago the River Mersey was one of the most polluted rivers in Europe suffering from effluent discharges from manufacturing, wastewater from large urban areas and discharges from the petrochemical and heavy chemical industry. By the late 1950s, no fish were present and the river was ecologically dead.

However, with the help of a range of organisations, authorities and communities, and stricter industrial standards, water quality has improved to such an extent that in the mid-1990s migratory salmon, an indictor of good water quality, were thought to be returning to the Mersey catchment. Video evidence confirmed the return of salmon to the River Mersey in 1999 and in 2001 the first salmon caught in the River Mersey for 60 years was captured in a fish trap in Warrington.