Fish are being left to die in canals that have become suffocated by duck weed, anglers have claimed.
Members of the Valley Carpers said Torfaen council is not dealing quickly enough to clear waterways around Cwmbran that are swamped in weeds.
They said they have found dead fish in the canals and have now taken to clearing the water by hand.
Torfaen council said it had been in talks to arrange a meeting “at the earliest opportunity”.
Recent sunshine has seen the floating weed spread rapidly into a green carpet across the slow-moving water along parts of the Monmouthshire and Brecon canal system.
“The canal is so full of duck weed, it is stopping the sunlight penetrating the water and the fish are struggling,” said Kevin Putnam, a member of the Valley Carpers.
- Bioluminescent plankton lights up Welsh coast
- Toxic algae shuts Cardiff lake
- Duck weed ‘explosion’ swamps canals
Duck weed is not harmful to humans or animals but if left to thrive, thousands of tiny plants can accumulate and starve the waterway of oxygen and sunlight.
“The council said they’re going to do it in winter. But by winter it’s going to be too late, the fish will be dead. It’s very frustrating,” said Tyron Mapp, another club member.
“That’s why we decided, as a group, to get in here and clear it ourselves.”
The group has cleared an estimated quarter of a tonne of weed in just two evenings at Pontnewydd as well as other items dumped in the canal.
However the problem has also spread close to a £1.4m restoration project at Ty Coch Lock.
Tofaen council said it was “committed to maintaining a balance” between ecology and the needs of local people both socially and economically.
Councillor Fiona Cross said: “Environmental conditions have clearly allowed this species to proliferate at the expense of others and, as with all semi-natural habitats, the canal requires some management.”