A woman who finished an epic 120-mile swim down the River Thames that saw her rescue a drowning cow while dressed as a mermaid declared Marlow to be the cleanest stretch of the river.

Keen swimmer and activist Lindsey Cole swam from Gloucestershire to London to raise awareness of plastic pollution.

Her journey was inspired by a trip to Bali where she saw mounds of plastic floating in the ocean while learning to free dive three miles from the shore.

Lindsey said Oxford had one of the most polluted sections of the river while the water was cleanest in Marlow, Windsor and Maidenhead.

She said: “In some areas, the river was quite clean but Oxford was a big surprise.”

The 35-year-old was congratulated by family and friends at the finish line in Teddington, south London, on Saturday when her 22-day journey came to an end.

Brave Lindsey managed between three and six miles per day while dressed in her mermaid’s tail – and even saved a cow from drowning in a weir during her journey.

She said: “I felt a bit sad to have finished the journey – I spent Sunday and Monday sitting on a couch.

“We swam through areas with no civilisation – it was quite tough.

“I couldn't eat for the first week or two because I was nervous and anxious and I got quite a lot of sores on my neck from the two wetsuits I was wearing when I turned my head to swim.

“The first day, I swam ten miles – the water was seven degrees and it felt freezing at the beginning but my body became acclimatised to it.”

Lindsey swam alongside a giant mermaid sculpture – made from plastic bottles – aboard her support boat which was manned by 38-year-old artist Barbara de Moubray.

The environmentalist wanted to raise awareness of pollution from single use plastic by collecting all the waste she found in the water on her journey.

But she had not anticipated sparking a rescue mission two days into her journey to save a stranded farm animal she encountered in Oxfordshire in early November.

Lindsey said: “Barbara thought she saw a big sheet of plastic and rowed towards it.

“Then we realised it was a cow which had been stuck in the mud overnight and was resting its chin on a branch trying to remain calm.

“It was really sad, she was submerged in the water except for ten inches of her upper back.

Lindsey called the fire brigade and a specialist rescue crew used a hoist to haul the cow out of the water before it was reunited with its two calves.

Lindsey and Barbara stayed in hostels and was also put up by people who responded to her Facebook ad for a place to stay, and said some people even dressed up as unicorns and mermaids as they watched her pass by.

She said: “The support from people was a highlight for me – some people even jumped in the water to swim with us.

“We were our own support crew so we had to find somebody to help us move our car to the next stop each morning before we started to swim, which contained all the rubbish we had collected.

“When I swam through the towns, I would keep my mermaid's tail on where the children liked it.”