Rescue teams were called in after a porpoise was found stranded on a north Norfolk beach.
A member of the public spotted the distressed aquatic mammal on the sand on Wednesday morning.
Jerry Woodley, Sheringham and Cromer Coastguard Sheringham station officer, said they were called at about 10am, and members of British Divers Marine Life Rescue were also alerted.
Mr Woodley said: "The first shout was there within about 20 minutes and they were able to keep this mammal hydrated by pouring water over it, after direction from Marine Life Rescue.
"Once they arrived, they got suited in their dry suits. The mammal was distressed, but once they reduced its heart rate they brought it back into the North Sea, and it swam away quite happily.
"It's a good result. With the recent whale strandings it's nice to get a happy ending."
The carcasses of several sperm whales washed up onto north Norfolk beaches late last year. These animals, which were believed to have been part of a pod of young males who got lost on the journey to breeding grounds in the Atlantic, were found in The Wash and at Sheringham and Weybourne.
Although porpoises look similar to dolphins, they are more closely related to narwhals and belugas.
The most common species found around the British Isles is the harbour porpoise, which grows to around six feet in length.
Anyone who spots a porpoise or other animal in distress on the beach should contact the Coastguard on 999.
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