A woman sneaked into the seal pool of Berlin Zoo on Monday night, risking serious injury to take a swim with the animals after closing time, zoo authorities said.
A witness told German daily Bild: "I watched as the woman stripped to her bikini and then lowered herself into the seal pool. Further back was a man taking photos."
Zoo staff failed to catch the woman, said Ragnar Kuehne, a zoo manager, but would have called the police if they had.
"The woman could have been seriously injured if the seals had bitten her," he said.
The woman took her swim at 1930 CET, half an hour after visitors had been ushered out.
"People need to respect animal welfare in both the wild but also in captivity," said Doerte von der Reith, spokesperson for the International Fund for Animal Welfare. "To intrude into their compound is absolutely irresponsible."
Gloria and Grania are not yet fully grown. Fur seals can vary in size from 1 to 3 meters. The pair moved to the German capital from Hanover Zoo in 2013.
Berlin Zoo's most famous resident was polar bear Knut, whose mother rejected him as a new-born leaving the fluffy white cub to be reared by a zookeeper. Thousands of visitors queued for hours to watch him frolic in his enclosure. The bear died suddenly of an epileptic fit in March 2011.