“Otto was beloved by park staff and guests alike,” Bays Mountain Park and Planetarium in Kingsport wrote in a Facebook post on Thursday﻿ . “A cheerful creature, he could often be found swimming or playing with toys in his pool, even when it was snowing outside.”

A young river otter at a Tennessee nature park is dead after park visitors threw food intended for humans into his enclosure.

A necropsy to determine the exact cause of death is still forthcoming, but the park had said in a post earlier that day that Otto “fell ill after park guests threw food into his enclosure that his body could not tolerate.” He was taken to a veterinarian, but died within hours.

The park had various signs and postings instructing visitors not to feed the animals, a representative told HuffPost in a Facebook message. The rep said staff could not be sure exactly what Otto ate that made him ill.

“Grapes were found in the enclosure, but we suspect other food likely was also thrown in,” the rep said.

Park manager Rob Cole told the Kingsport Times-News that “grapes aren’t part of their diet and it’s not what we feed them. Even the most well-intention efforts to feed them is not a good idea and we’re dealing with the aftereffects now.”

The park took the opportunity to remind visitors not to feed its animals.

“Human food is often intolerable and, in this case, even harmful to our animals,” the park’s Facebook post about Otto’s death read.