A SeaWorld animal rescue team was threatened by onlookers while attempting to retrieve a stranded sea lion earlier this week. KTLA reports that on a trip to the end of Santa Cruz Avenue in Ocean Beach, California, where a 1.5-year-old sea lion had wandered into the sand beneath some cliffs, SeaWorld employees heard disapproving murmurs from hecklers above them. At a certain point, someone threw a rock.

“Thank goodness it didn’t make contact, but it definitely created a hostile environment where we no longer felt safe,” Kortney Sanders, who took part in the rescue, told KTLA. “It’s really disappointing. It kind of breaks my heart.”

Returning to the beach about an hour later, this time in the company of several San Diego police officers, SeaWorld employees ultimately succeeded in retrieving the sea lion and bringing it to their critical care unit. The animal has since been diagnosed with a fever and severe pneumonia.

SeaWorld employees told KTLA that they’ve been exposed to heightened levels of harassment from the public following the release of Blackfish, the 2013 documentary that openly criticized SeaWorld and the treatment of orca whales kept in its care. (The documentary was produced, in part, by CNN.)

Outside’s July feature on the experience of animal care workers at SeaWorld explored the trials and successes of caring for captive animals.