A zoo is to take legal action against a group of YouTube vloggers who entered the attraction and allegedly startled a rare zebra.
Authorities at Chester Zoo condemned the group's actions after they posted footage of their trespassing online.
A spokesman said the group had "little or no regard for their own safety, or the safety and welfare of the animals".
Lawyers for the zoo said legal proceedings have started in the Business and Property Courts.
The action could result in an injunction preventing the group from entering the zoo again.
The zoo said property was damaged in the incident, which happened about two weeks ago.
The group were believed to have been taking part in an "overnight challenge", where people post videos of risky stunts on the internet.
Jamie Christon, chief operating officer at the zoo, said: "It appears the group startled a Grevy's zebra, an endangered species which we care for as part of a Europe wide breeding programme, as the animal had an injury to its hind leg following the trespass.
"Thankfully the animal has since been making a good recovery."
Trespassing on the site was "unacceptable and extremely dangerous", Mr Christon said.
He added: "We condemn the irresponsible actions of the group and are taking the matter extremely seriously."