Their aquatic skills and balancing prowess draw thousands of visitors to Britain's largest zoo each month. But it has emerged that the crowd-pleasing performances of Whipsnade Zoo's five Californian sea lions were unexpectedly put at risk when they developed eyesight problems.
The deterioration in their vision was caused by rises in chlorine in the pool where Dom, Bailey, Lara, Kyra and Salt perform their popular Sea Lion Splash show, a safety inspection report has revealed.
In March last year, the zoo, based in a 600-acre park in Bedfordshire, reopened the sea lions' pool after a major revamp. But, says the report, when the sea lions returned after two-months at London Zoo, their vision began to fail due to problems with the pool's water-filtration system.
The worst affected was Salt, a 26-year-old veteran, "possibly due to her previous exposure and age".
Whipsnade responded by placing the filtration system under review for six months. At the same time, vets made regular checks on the five mammals' eyesight due to the "fluctuations in water quality".
A zoo spokeswoman said this weekend that no further problems had been identified. She added: "Our staff really are committed to providing the very best care for our animals."
Whipsnade's safety inspection report was released to The Independent on Sunday by Central Bedfordshire Council following a freedom of information request.
Details of the incidents appear in a document compiled by the local authority this March, ahead of a renewal of Whipsnade's zoo licence. The inspection also revealed that in January four of the zoo's rockhopper penguins were killed by a fox that got in via a damaged electric fence, and that six lemurs had escaped via an open drawbridge. They were lured back by keepers.