An invasive breed of salmon – which has spread from Russia – is colonising Britain’s rivers and putting native fish at risk.

In 2017, ‘unprecedented’ numbers of the Pacific pink salmon were seen in British waters, where they successfully spawned.

And now after two years out at sea, the Environment Agency is warning that more pink salmon will return to British waters this year to spawn.

An invasive breed of salmon - which spread from Russia - is colonising Britain's rivers and lakes. (Pictured: The invasive Pacific pink salmon, photographed here in Khabarovsk, far East, Russia)

Their presence is said to be threatening native fish (Pictured: An unidentified salmon leaps its way up the river Tyne in Hexham, Northumberland)

The danger is that they will introduce diseases or parasites that could afflict Britain’s native Atlantic salmon and wild trout and compete with them for food.

Pink salmon are native to the icy waters off Alaska and Canada but they were introduced to Russian rivers in the 1960s and came to Britain after spreading across northern Norway.

In 2017, seven pink salmon were recorded on the rivers Wear, Tyne, Coquet, the Humber, Hampshire Avon in Dorset, Frome and from the mouth of the Solway estuary.

Pacific pink salmon are smaller than Atlantic, and sometimes have a hump on their back. They are steel blue or blue-green with silver flanks and white bellies.

They also have a distinctive black tongue, and are about 40-60cm (16-24ins) in length.

The Pacific pink salmon are smaller than the Atlantic, and sometimes have a hump on their backs. The fish are also steel blue with silver flanks and white bellies. (Pictured: Pacific pink salmon at Port McNiel, northern Vancouver island, Canada)

After they were seen in 'unprecedented numbers' in 2017 the Environment Agency has warned, two years later, that large numbers of the fish are likely to return to shore. (Pictured: Salmon in Seattle, US, in 2017)

The Environment Agency said: ‘Owing to the two-year life cycle of this species, 2019 will be the first year that we can expect to see these fish return in numbers.’

Simon Toms, of the agency, added: ‘Anyone catching a pink salmon is urged not to return it to the water, but to report it, photograph it and freeze it.’

There have been ten confirmed sightings across Britain this year, including one in Wales, three in Scotland, and two off the Northumbrian coast.