A project to identify and tackle sources of pollution on the River Ely could set a precedent for restoring other water courses across Wales, it has been claimed.
A “massive survey” of the river found hundreds of fly-tipping hotspots and previously unknown sewage pipes.
The Restore our Rivers campaign will now set about tackling the problems.
Water quality in parts of the river had been classified as “poor” and “bad” by Natural Resources Wales.
The Ely flows for about 24 miles (39km) from south of Tonypandy, Rhondda Cynon Taff, and then through the city suburbs of Pentrebane and Caerau into Cardiff Bay, passing landmarks like the Museum of Welsh Life at St Fagans and Cardiff City Stadium.
An inquiry into pollution on the river was initially carried out by Cardiff council’s environmental scrutiny committee after complaints from anglers that the upper reaches of the Ely were devoid of fish and wildlife.
Several organisations including Natural Resources Wales, Dwr Cymru, Keep Wales Tidy, South East Wales Rivers Trust, Cardiff Rivers Group, Glamorgan Anglers and Groundwork Wales came on board.
The intensive survey carried out along the Ely and its tributaries was the first of its kind on a Welsh river.
Councillor Paul Mitchell, chairman of the environmental scrutiny committee, said it had highlighted the “devastating impact” litter and other forms of pollution was having.
“We found hundreds of major tipping incidents and very large objects in the river, people travelling across three or four fields just to throw a trolley in the river,” he explained.
“We also found sewage outfalls that Dwr Cymru Welsh Water were not aware of because they inherited an antiquated Victorian system.
“And further up in the catchment we saw the effects of unscrupulous builders who deliberately misconnect showers and granny flats directly into the storm drains so they don’t have to pay connection fees to Dwr Cymru.
“It all adds up to kill a river off and it’s about time we did something to sort it out.”
A number of projects, involving school and the community, will now be carried out to target the issues raised in the survey.
Keep Wales Tidy, which lead the work of compiling the survey, is now preparing an online resource, mapping pollution points along the river.
Pam Bacon, from the charity, said the partnership approach between different organisations, the council and community “had to be the way forward”.
“It’s a way of getting that pride and awareness back about the value of our rivers but also show what the different organisations are doing to tackle their own issues,” she said.
Imogen Brown, head of Dwr Cymru Welsh Water waste water networks, said the survey had provided “fantastic information”.
“We have 7,000km of rivers in Wales and we can’t understand everything that’s going on in all of them – so this survey will really help us understand if we’ve got misconnections going into there or problematic assets.”
The restoration work was launched on Tuesday with a litter pick along the banks of the river at Grangemoor Park in Grangetown – 40 bags were collected – and this will continue throughout the spring.