Two rehabilitated beluga whales have taken their first swim in an Icelandic open water sanctuary, the charity Sea Life Trust has said.

The pair, named Little Grey and Little White, were able to explore the wider natural surroundings of Klettsvik Bay on Heimaey, one of the Westman Islands off the south coast of Iceland.

The bay is approximately 32,000 square metres – which is equivalent to the size of around 117 tennis courts – with a depth of up to 10 metres.

The Trust said the whales had made good progress since moving to bayside care pools in August, and the swim is the part of a carefully managed programme to ease them into the wider sanctuary.

They will return to the sanctuary care pools over a short period of time and their health and well-being will be assessed on a daily basis.

Andy Bool, head of Sea Life Trust, said: “We’re absolutely thrilled by the progress that Little Grey and Little White have made since moving to their bayside care pools.

“They are feeding and acclimatising well to the more natural surroundings as well as all of the outdoor elements.

“We are introducing them gradually to the bay in little steps, but seeing them swim together and deep dive amongst the flora and fauna of the wider bay for the first time was amazing to witness and gave us a real sense that Little Grey and Little White are enjoying being back in the sea.”

The Beluga Whale Sanctuary, operated by the charity, was created in partnership with Whale and Dolphin Conservation (WDC) and is one of the biggest developments in captive whale and dolphin care and protection in decades.

Cathy Williamson, WDC’s End Captivity programme lead, said: “We’re delighted that Little Grey and Little White are now exploring the wider bay and adapting well to their new, natural, stimulating environment.

“We hope this will mean that many of the more than 3,500 whales and dolphins held in captivity for shows and swim with attractions can be brought to sanctuaries to live more natural lives or be rehabilitated for a return to the wild.”

Little Grey and Little White’s journey back to the ocean will be told as part of a new two-part documentary which will be shown on ITV this October.

The programme will show the complexities and dedication around the world-first project and will feature comedian and animal lover John Bishop.