© MasonsBehan the rhino with her new calf at Whipsnade Zoo
The keeper was tramped by the beast as he tended to a rhino and her calf early this morning.
It's not clear what caused the animal to attack.
The man, who is in his 50s, suffered chest, abdomen and pelvis injuries after the animal attacked inside its enclosure.
He was helped out of the water by zoo staff, and was taken by ambulance to Addenbrooke's Hospital in Cambridge in a serious but stable condition.
He was given pain relief at the scene for his injuries
A Whipsnade Zoo spokeswoman said: 'At approximately 8.15am today one of our keepers was injured at Whipsnade Zoo.
'Emergency services were immediately called and the keeper involved was treated by paramedics at the scene and has now been taken to hospital.'
Dave Tamarro, of the East of England Ambulance Service NHS Trust, said: 'When we arrived it was clear that the patient had received a number of injuries, including injuries to the chest, abdomen and pelvis.
A Bedfordshire Police spokesman said: 'We were called to Whipsnade Zoo at around 8.25am. Our role was to assist the other emergency services.'
Comment: Zoo animals often exhibit strange behaviors due to humans forcing them to live in unnatural habitats, and the suffering that ensues is on display most starkly there. However animals throughout the world have been acting strange and aggressive, and there have been increases in family pets attacking their owners often without provocation. Are animals reflecting the increasingly odd behaviors in the human population?