Tenby's 'Wally the Walrus' has disappeared after being inundated with tourists over the Easter bank holiday weekend.
The Arctic walrus was first spotted in Ireland before making its way to Pembrokeshire last month.
Animal welfare groups monitoring the animal believe it came across the North Atlantic Ocean from Greenland on an ice floe.
Since appearing in Wales, the animal has become a local celebrity - drawing crowds over the Easter weekend, with many getting 'too close' and some driving from as far as Essex.
The animal was left 'obviously disturbed' after being hassled by paddle boarders, jet skis and even people swimming out to get close to it, Welsh Marine Life Rescue told ITV News.
They said Wally has not been spotted since early morning on Easter Monday.
Terry Leadbetter, coordinator and founder of Welsh Marine Life Rescue said: "It was an absolute nightmare trying to keep people away.
"There were even people flying drones trying to get close. People were getting within a couple of metres of the walrus."
The Welsh Marine Life Rescue is warning people to stay away, reminding visitors that the wild animal is unpredictable.
He has been constantly harassed by people.
Terry added, "Wally was aware that people were there and was obviously disturbed.
"Walruses have been known to attack boats and they've been known to kill people so like any other wild animal you don't want to get too close just incase.
"These people are just going up to it and taking their chances. They are unpredictable, and you don't know if they are likely to turn around and attack someone or not.
"Someone who is acting irresponsibly could get injured."
Last month, 'Wally' was captured capsizing a dinghy boat before attempting to climb onto a fishing boat moored in the Tenby harbour.
When the walrus was first spotted, it was thought to be underweight.
Since then the animal has gained weight after discovering great feeding grounds around the Pembrokeshire coast.
It is thought Wally is less than two-years-old and still growing.
The constant need for food is thought to be one of the reasons for it leaving - or the busy flow of visitors.
The Welsh Marine Life Rescue said, "We believe that people have been breaking Covid restrictions by crossing the border from England to see the animal.
"There was one report that someone even travelled from as far as Essex and many people weren't sticking to social-distancing."
People are being urged to stay away from the walrus if it returns.