Campaigners say much more needs to be done to prevent storm sewers in Wales emptying into rivers and seas.
It follows ongoing concerns about raw sewage discharges into the River Conwy following heavy rain and storms.
An analysis of the 1,000 combined sewer overflows (CSO) monitored by Welsh Water has revealed that there were 30,000 similar incidents across Wales in 2017.
The water firm said without the releases, sewage would flood homes.
Stuart Llewellyn, who is chairman of the Llanrwst Anglers Club, said he had witnessed the overflow in the town operating on three out of four days in the last week.
It means untreated sewage is going straight into the river.
Welsh Water's own figures for 2017 show the overflow in the town was used 110 times - for more than 350 hours during the year.
An overflow at the beach resort of Pendine in Carmarthenshire released combined sewage on 317 days of the year.
Another CSO at Tintern in Monmouthshire discharged waste water on nearly 250 occasions.
In a single year, across all of Wales, combined sewage overflows operated for the equivalent of 6,800 days.
"It's incredible. These are supposed to be exceptional event discharges, they are not supposed to be every time it rains," said Mr Llewellyn.
"As we know, rain in Wales is not an exceptional event."
He has called on Welsh Water to improve facilities at the town's water treatment plant, including increasing capacity for storage in storm tanks.
"We are concerned about all rivers in Wales," he added.
"Our rivers in Wales are deteriorating, they are declining year on year, and we need to start addressing the issues."
Welsh Water said that as a company closely associated with the environment it was "very aware of the impact our work has on our surroundings and take our environmental performance very seriously".
The company said it will have invested £460m in water services in the last year which was part of a £2.3bn investment over a five year period by the end of 2020.
It includes work in Carmarthenshire and Cardiff to help prevent surface water getting into the sewer network in the first place.
The £95m Rainscape scheme in Llanelli is credited with helping save the town from the worst effects of Storm Callum in November last year, by helping divert and slow down water running off homes and streets.
However, it has not prevented some stinging criticism.
TV wildlife expert and presenter Chris Packham called the situation in Llanrwst "Victorian" in a post on Twitter.
Officials from the Llanrwst Anglers are due to meet with representatives from Welsh Water on Monday to air their concerns.