A famously polluted canal is now supporting one of the fastest growing fish populations in the UK, experts say.
The canal was once so polluted it was "in danger of catching fire"
The water quality is so good in the Manchester Ship Canal after a three-year clean-up initiative that it now supports more than 30 species of invertebrate and fish compared with fewer than five in 1991.
At one time the canal was so polluted with industrial waste and domestic sewage there were reportedly signs on the banks warning people not to smoke because of the flammable gases rising from the water.
And as recently as the 1990s, fish could not thrive in some areas because the water was clouded with algae which deprived other aquatic life of oxygen.
But a project to pump liquid oxygen at a rate of up to 15 tonnes a day into the worst polluted area of the canal has seen a boom in biodiversity, the Mersey Basin Campaign (MBC) revealed on Monday.
The £4m operation, which began in 2001, has been taking place on a two-kilometre stretch of the canal, at Salford Quays.
It has enabled fish such as roach and perch to start spawning again, according to water quality experts Apem.
The rate of population growth among fish, particularly roach, "are amongst the highest to be found anywhere in the country, if not the highest", Apem said.
Dr Keith Hendry, managing director of Apem, said: "The success of the oxygenation project proves what can be achieved when organisations work together and the money is there for investment.
"What has happened to the water ecology is little short of astounding."
Walter Menzies, chief executive of MBC, said work needed to continue to build on the success of the project.
"This is a minor miracle in environmental terms, but it's still only a stop-gap measure that will buy us a decade or so of breathing space," he said.
"We estimate that we'll need a massive investment of several billion pounds in our water infrastructure before we can switch the oxygenation system off."