The three girls, who tripped from the ride, were rushed to Capital Hospital and the critically injured one put on Oxygen support, police said.
The girls, students of Ramadevi Women's College here, went to the Park on the occasion of Raja festival holiday.
They hailed from Niladri Vihar area in the city.
The privately run amusement Park authorities confirmed the incident.
"It was an unfortunate accident. We had throughly done the checking of the water slide," M Kumar, the chief security officer of the park, said.