But now Otto’s days of delighting visitors are over.

In a Facebook post Thursday, the park announced that Otto fell ill and died after “guests threw food into his enclosure that his body could not tolerate.” It is not yet known what the otter may have eaten, but grapes, which are not part of the semiaquatic mammal’s usual diet, were found in the habitat, park manager Rob Cole told the Kingsport Times-News. A necropsy is being done to determine an exact cause of death.

“As a reminder, feeding the animals at Bays Mountain Park is strictly prohibited for exactly this reason,” the park wrote on Facebook. “Human food is often intolerable and, in this case, even harmful to our animals.”

Park staff grew concerned about Otto last week when the 2-year-old otter stopped behaving like his usual self, Cole told the Times-News on Thursday.

“Otto exhibited initially what we thought were balance issues,” Cole said. “He wasn’t real steady on his feet and his condition hasn’t improved, so it was time to make sure all is well and that Otto would be okay.”

That same day, the otter was taken to an animal hospital at the University of Tennessee for treatment. But within hours, the park shared a grim update on Facebook.

“We’re deeply saddened to announce that Otto the river otter did not make it,” the post read, noting that the critter was “beloved by park staff and guests alike.”

Cole said that once Otto’s body is released, he will be taken back to the park for a private burial.

Otto first came to Bays Mountain in October 2017 when he was 9 months old after he and his sibling lost their parents in a flood, the park said. The two orphaned pups were initially cared for by a rehabilitation center in North Carolina with the goal of one day releasing them back into the wild. However, the young otters lost their fear of humans, so Otto was moved to the park instead, where it didn’t take long for him to become a crowd favorite for his sociable nature. Posts on the park’s Instagram page show the otter balancing on a bright orange inner tube in the middle of his pool and propping himself up against a chain-link fence to “pose” for a picture.

While some fans flooded the park’s Facebook page with memories and photos from their visits, others expressed outrage that people disobeying the rules may have led to Otto’s death.

“Absolutely heartbreaking,” one person commented on Facebook. “A sweet, innocent animal gone because of stupidity. Very sad.”

On Twitter, another user wrote, “If you need me I will be crying about Otto the Otter from Bays Mountain for the next 10 years.”

The park, which has exhibits for creatures ranging from wolves to snakes, notes on its website that all its animals are fed “nutritious diets.” Otters normally eat fish, crayfish, meat and eggs.

“Grapes aren’t part of their diet and it’s not what we feed them,” Cole, the park manager, told the Times-News. “Even the most well-intentioned efforts to feed them is not a good idea and we’re dealing with the after effects now.”

Otto’s death is just the latest example of what can go wrong when visitors don’t follow the rules at zoos or other wildlife preserves. In perhaps the most infamous case, Harambe, a gorilla at the Cincinnati Zoo, was fatally shot in 2016 to save the life of a toddler who crawled past a barrier and fell into the animal’s enclosure. Just last month, a flamingo at a zoo in Illinois had to be euthanized after it was injured by a child skipping rocks into its habitat, The Washington Post’s Eli Rosenberg reported.

It is not clear whether the Tennessee park has plans to take action against the person or people who allegedly threw the food into the enclosure, but it said Otto’s fate should be a cautionary tale.