Three members of staff at Blackpool Zoo were taken to hospital after a chemical leak close to the sea lion pool.
The employees were taken to Blackpool Victoria Hospital on Sunday afternoon as a precaution after there was a “small” leak of chlorine from a pipe.
One fire engine and a duty officer also attended the scene at around 3pm, to provide support to zoo officials due to the nature of the incident.
The sea lion pool had to be cordoned off to the public for a time, also as a precaution, but it is understood the sea lions themselves were unaffected.
Blackpool Zoo is home to the largest sea lion enclosure in the UK and eight years ago it was transformed from drab concrete to a natural, modern and sea lion-friendly environment.
The zoo said all measures were taken as a precaution.
A spokesman said: “The pool was re-opened after a period of time.
“No one was injured but the staff were taken to Blackpool Victoria Hospital as part of our procedures.
“The fire brigade was called as a precaution because a chemical was involved.”
A spokesman at Blackpool’s Forest Gate station said the leak was “small”, adding: “We were there in a support capacity but it was dealt with by zoo staff.”
The incident follows another occurrence at the sea lion enclosure in July when the a broken filter system and the hot weather caused the pool to turn green.
Chlorine is used as part of a complex water treatment system to ensure the water in the pool is kept free of any micro organisms that may be harmful to the animals.
Larger doses of the chemical can cause irritation to eyes and lungs.