A broken filter system and the hot weather caused the sea lion pool at Blackpool Zoo to turn a deep green colour.
Weekend visitors were told the off-colour was caused by algae and that no harm would come to the animals, with the pool drained overnight and the system fixed yesterday.
One of the zoo’s Californian sea lions was pictured sunbathing beside the pool while covered in white patches – but that was caused by gradual moulting, which the animals do once a year, a zoo spokesman said.
In a statement, the zoo said: “A fault with the pool system has now been repaired. The sea lions are currently moulting which can cause patching to appear.
“ Our staff are always happy to answer visitors’ questions.”
A sign posted close to the sea lion pool said: “Due to unforeseen technical issues with our pool filtration combined with the prolonged warm sunny weather, our pool has gone green with algae.
“This causes no harm or health issues to our sea lions and we aim to rectify the issue as soon as possible.”
A dead wild mallard (inset) was removed from a pond close to the sea lion pool, which was also green, after being reported by a visitor.
A spokeswoman said what killed the duck, which did not belong to the zoo, was not known.
She said staff did not believe any of the algae seen at the attraction was toxic.
The Environment Agency said blue-green algae, or ‘cyanobacteria’, can produce harmful toxins, but said it is impossible to tell if algae is toxic just by looking at it.
It said: “Algae occur naturally in inland waters such as rivers, streams and lakes. When conditions are ideal for growth, an algal bloom can occur.
“During a bloom, the water becomes less clear and may look green, blue-green or greenish-brown.
“Scums can form during calm weather when several bloom forming species rise to the surface. This can look like paint, mousse or small clumps.”
ELEPHANT JOURNEY FOR BBC
The zoo’s mammoth new residents are the subject of a new TV show telling the tale of their move from Twycross to their new state-of-the-art home.
BBC programme Elephants On The Move goes behind the scenes at Twycross as the four female elephants – Minbu, Tara, Noorjahan and Esha – journey to Blackpool as part of a European breeding programme. They are now living in the new multi-million pound elephant house, which opened earlier this year.
The documentary will air on BBC One as part of the Our Lives series from 7.30pm on Monday, though it is already available to watch on the BBC iPlayer.