Police investigating the deaths of a couple whose bodies were discovered in a fast-flowing river in north Wales say their deaths are being treated as an "unfortunate tragic accident".

Witnesses had seen the man and woman, who were in their 20s, walking dogs by the river Clywedog in Wrexham, which was swollen following the torrential rain. But police were not able to verify reports they had been trying to rescue a dog from the water.

The deaths came as thousands of people around the UK were affected by flooding in the worst September storms for 30 years, although forecasters said the worst of the rain was over.

The body of the first victim, named locally as Alicia Williams, 27, was found on a sandbank in the river, at Erdigg, during the early evening. Her 25-year-old partner David Platt's body was discovered downstream seven hours later following an extensive search by about 20 police, firefighters and volunteers from mountain rescue.

Residents said Platt worked at a local farm constructing children's playpens and the couple had recently had a baby daughter. Other locals described the river's levels in recent days as "horrific", saying it had risen 4ft (1.2m) since the heavy rainfall.

North Wales police said there were no witnesses to say whether one or both had gone into the water to retrieve a dog, so it was impossible to speculate how they ended up there. Two bouquets had been left at the side of a gate.

Michael Morgan, who works at a car wash close to the entrance to Erddig country park, said he was alerted by a whippet that licked his ear as he buffed a car. "I thought it was a stray at first and was going to tie it up." But he realised the dog was in a beautiful condition, so went up to a field to have a look for the owner.

He went into the park and saw three more dogs, two retrievers and a Jack Russell, sitting beside a Citroën Picasso, which is thought to have belonged to the couple. The two retrievers were wet up to their heads. He saw the woman's body and said he recognised her as a dog walker in the area and it had been a terrible shock.

Detective Chief Inspector Mark Pierce of North Wales police said causes of death have yet to be established. Families of the couple were going through indescribable grief, he said. Pierce said the likely scenario is that "there was unfortunately a tragic accident".

Elsewhere, homes, roads and the rail network in northern parts of England and Wales continue to be affected by flooding. In York, the River Ouse was stabilised, as towns and rivers in North Yorkshire were warned of the risk of flooding by the Environment Agency.

There are still 36 flood warnings in place, chiefly in the north east of England where 27 such warnings continue, with seven in the north west, one in the Midlands and one in Wales. The number is expected to fall as the rain eases.

The Environment Agency said about 570 homes and businesses had been flooded across England and Wales since Sunday, including 300 homes in Yorkshire. It warned communities in North Yorkshire to stay alert and prepare for the risk of flooding, as rivers peak at record levels. Emergency teams worked overnight on Wednesday to shore up river defences and pump out floodwater.

The River Ouse reached its peak at more than 5m above normal levels on Thursday. Yorkshire Water said river water was overloading sewers and that its pumping stations were working to full capacity. Thousands of sandbags were delivered to the village of Cawood, Yorkshire, which was in danger of flooding.