One of Wales' largest surf schools has had to close its doors due to raw sewage being pumped into the sea nearby by Dŵr Cymru.

Porthcawl Surf School released a statement on their Facebook page saying that they've been forced to cancel all lessons today and tomorrow (August 18 & 19) because of raw sewage being discharged into the sea.

The campaign group Surfers Against Sewage, which monitors the dumping of untreated waste water around Britain, has sent a warning out to people hoping to enter water in Porthcawl because of sewage discharged at both Rest Bay and Sandy Bay.

In their statement, Porthcawl Surf School said that "Welsh Water has dumped raw sewage into the Severn Estuary. Particularly affected is Rest Bay and Sandy Bay. Due to the risk to health, we have decided to close the surf school on Thursday and Friday. We have canceled all our surf lessons and will not be renting any equipment. It will take a couple of days for the pollution to be dispersed and we hope to open again for the weekend."

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Most rain water enters sewers where it's combined with waste water from homes and businesses. When the capacity of these sewers is reached, for instance after heavy rain, their design means that the additional flow is discharged at certain points in the system either into rivers or the sea.

Because of the recent spell of dry weather, sudden downpours aren't absorbed as well by the ground, meaning more rainwater ends up in sewerage channels leading to the diluted effluent being discharged into rivers and the sea.

Porthcawl Surf School is open year round and provides lessons to all levels of surfers, although the summer holidays would be considered their peak period.

On Tuesday afternoon, the Surfers Against Sewage 'Safer Seas' app sent out an alert regarding the sewage discharge. 

In response to comments on Twitter, Dŵr Cymru blamed the discharge of untreated waste water on heavy rain, stating: "Despite the widespread rain, only two of our combined storm overflows (CSOs) operated at designated bathing waters.

"This is how they're designed to operate when the wastewater network in an area reaches capacity due to the volume of rainwater in it. The spills were compliant with our permit to operate them.

READ MORE: The legacy of a Newport site that still discharges toxic chemicals into the Severn

"Also, we sent notifications to Surfers Against Sewage so that they were aware and could notify their members. We appreciate that people have concerns, but they're essential to prevent sewage water from backing up into people’s properties during heavy rain."

Last year Dŵr Cymru paid three of its top executives performance-related bonuses of £931,000, nearly doubling the pay packets of chief executive Peter Perry, chief financial officer Mike Davis and executive director Chris Jones.

The performance-related bonuses were paid to the execs despite more than 100,000 instances of raw sewage being pumped into Welsh waterways over the preceding 12 months.