The river, which flows from Stockport through Manchester and Liverpool, was once a deadly cocktail of raw sewage and toxic chemicals and locals joked that you couldn’t drown in the Mersey because you’d die of poisoning first.
Dr Peter Jones of the Mersey Basin Campaign, a UK Government-backed movement to clean up the Mersey river system, said: “When I joined North West Water in 1974 the rivers in the Northwest were gruesome.
“Whether you looked at the chemistry or the biology, by any indicator the Mersey was as bad as you could get.”
Yet today the Mersey is flourishing after a decades-long clean-up and last year around 37 different species of fish were caught by anglers.
Mike Duddy, who works for the Mersey Rivers Trust, a charity that maintains the river for both local people and wildlife, told the Liverpool Echo that last year’s catch was nearly two and a half times the number of species found in 2002.
Mike said five different types of shark have been found – bull huss, tope, dog fish, smooth hound, starey smooth hound – as well as eels, sea scorpions, turbot, and smelt.
There are plans in place to make the River Mersey sewage-free by 2030. Liverpool City Region’s mayor Steve Rotheram says the city region will no longer invest in any projects which pump untreated waste into rivers.
His plans are backed by former Conservative environment minister Lord Heseltine, who helped establish the Mersey Basin Campaign Partnership.
He said: "The river today is an environmental success story but, as recent public anger over the discharge of untreated sewage into our rivers and seas shows, we cannot be complacent and must do all that we can to ensure we care for our great river."
Around six million litres of raw sewage – the equivalent of more than two Olympic swimming pools - was discharged into the River Great Ouse at Brackley, Northamptonshire, because of a malfunction of Anglian Water systems.
Fish including brown trout, chub and pike were killed, as well as smaller species such as bullhead, dace, stone loach, minnow, gudgeon and 79 brook lampreys. Dead signal crayfish were also spotted.
A dog walker saw up to 30 dying fish being carried by the river flow, gasping for breath belly-up or tail-up.