Day seal hopped on paddle board to play
'Dandie Dinmont' had been rescued by the RSPCA East Winch team and released him back into the Wash in November 2017
However, according to Skegness Natureland who had cared for him, he has only been seen hanging out with humans this year.
More than 25,000 watched a video posted on Facebook of Dandie hopping on a board during a lesson with the Yellowbelly SUP School in Anton's Gowt.
Instructor Phil May said the River Witham has been rich with wildlife this season, with lots of kingfishers, herons and fish - but he couldn't believe when the seal joined a lesson..
"We first spotted him when we were on the jetty and he swam past," recalled Phil.
"Robyn Smith was having her second lesson and as it was quite a windy day so we had found a more sheltered spot for the stand-up instruction.
"We hadn't seen him following us and it was quite a surprise when he crept on the back of Robyn's board.
"He was with us for about 10 to 15 minutes, rolling off one board and then onto another.
"I was just amazed because he hadn't been feeding or calling him.
"It felt quite an honour that he joined us - having a seal join us was certainly the .next level where wildlife along the river is concerned."
Although Dandie hasn't joined any more lessons, Matt Yeadon of Skegness Natureland warned anyone who spots the seal not to touch him.
"He has only taken to hanging out with humans this year, which hasn't been helped by the fact that people have been reported feeding him," he said.
"We would recommend anyone who sees him to keep their distance, as he is still a wild animal (despite his boldness).
"We would definitely say don't feed him - it could make him ill and he could also bite, which can cause a serious injury and infection.
"We'd suggest to try to not touch him, as he may feel threatened and bite.
"Don't panic if he gets close to you through choice or hops on your paddle board, but don't reach out to stroke him."