Nadia De Longhi, head of regulation and permitting at NRW, said despite “repeated warnings and interventions” Welsh Water had been “unable to reverse this concerning trend”.
“This has left us with no choice but to pursue a number of prosecutions against the company which have recently concluded,” Ms De Longhi added.
“This is not the outcome we want, nor the best outcome for the environment – our priority will always be to bring companies into compliance and prevent environmental damage from happening in the first place.
“Welsh Water must address the root cause of these pollution incidents and take preventative measures before more harm is done to the water environment.”
NRW added it would be increasing its capacity for monitoring and auditing discharges, as well as clamping down on unpermitted storm overflows and introducing tighter criteria for annual performance reporting.