Danny the dolphin was a popular sight in Portland, off the Dorset coast, entertaining locals with his tricks and coming close to boats, delighting those within.
However, experts now believe that the friendly mammal, found dead, was killed by a boat strike.
Portland Port said the body of a bottlenose dolphin was found in the water on Tuesday, and he has since been identified as Danny.
Locals and tourists alike are mourning the death of the creature, which had 4,500 fans on Facebook and was a popular draw for those on boat trips.
It is believed his death may have been caused by an accident with a boat, with a necropsy under way at the Zoological Society of London to determine the exact cause.
Dolphins who become too accustomed to human activities and therefore see boats as less of a threat - becoming used to the little tourist motors - are likely to be less wary around dangerous ships, conservationists have warned.
Marine wildlife expert Liz Sandeman, co-founder of Marine Connection, described the news as "devastating".
She said in a statement: "We've been studying solitary dolphins and whales for over 20 years and when I received the news, although I'm really saddened by it, I'm not surprised because the problem with solitary dolphins is they become habituated and they lose their wariness around vessels.
"It happens time and time again, they lose their fear among humans and end up very different creatures."
A spokesman at Portland Marina said: "We’re devastated to report that our resident dolphin Danny has been identified as the dead bottle nose that was recovered from Portland Harbour yesterday. The cause of his death is as yet unknown.
"Danny was well loved at the marina by staff, berth holders and visitors alike, he brought a little bit of magic whenever he came into the marina basin."
Danny, who is believed to be aged 12, was popular among watersports business owners along the harbour.
Dan Bell, of Jurassic Jetski Tours, who photographed Danny when he appeared alongside his tour groups told the BBC that the death was "very sad news".
"He was very friendly and playful. He would just pop up out of nowhere," he said.
Marine biologists believe tens of thousands of dolphins are killed by fishing boats every year, and have called for tougher regulation and CCTV cameras on ship to stop the destructive practices.
Earlier this week, three further dead dolphins were found floating off the Dorset coast, on Chesil beach, tangled in fishing nets.
A spokesperson for charity Blue Planet Society said: "The death, injury and strandings of cetaceans in EU waters is not documented by any official process or recording system. From our experience we would guess that tens of thousands of dolphins are dying each year.
"Only around eight-percent of dolphins killed at sea by the nets of fishing vessels reach the shore. The cetacean carnage witnessed recently on the south coast of England is just the tip of the iceberg.
"Despite the scale of the problem, dolphin bycatch is mostly being ignored by animal activists. Consequently public pressure is not influencing lawmakers as it has done for other animal welfare issues."