The Legoland Windsor attraction has closed abruptly due to a burst water main.
Customers were told to leave rides and exit the resort at lunchtime on Sunday.
Thames Water said it had to shut off the damaged main near St Leonards Reservoir to prevent flooding, which affected supplies to the theme park.
It said some local residents had reportedly suffered flooded gardens and it apologised for the disruption.
Merlin Entertainments, the operator behind Legoland, said it is continuing to work with local partners and thanked guests for their "patience and understanding".
One Legoland visitor, who came with her children from Cornwall, said the sudden evacuation felt "surreal".
The woman, who asked not to be named, said: "We were queuing for a ride and had got right to the front when, all of a sudden, everything stopped moving.
"Then they came out and said, 'Right, come on, everybody off.'
"Over the announcement system, they said there had been some sort of Thames Water disruption in the local area and they didn't have any water.
"We'd booked a night in the hotel and stayed there last night, so we're absolutely gutted because we've just had to drive home.
"It's a good five-hour drive to come up for a nice day, only to come back after half a day."
Thames Water said supplies had been restored and repairs were under way. It said it would provide an update on Monday.
A spokesperson for Merlin Entertainments said the resort was closed while Thames Water worked to restore normal service.
"We apologise for the inconvenience and thank our guests for their patience and understanding," the group said.
The BBC understands the resort will reopen on Monday under normal operating hours.