The deceased have been identified as Bhavnaben Thakor (13), Poonamben Thakor (14), and Payal Thakor (15), a Radhanpur police official said.
Locals fished out the body of the three girls, said police.
Patan is among two districts -- the other being Banaskantha -- which has been badly hit by floods in Banas and its tributary Sipu river due to the heavy rains in the region and neighbouring Rajasthan.
State Emergency Operations Centre has said that a total 225 people in the state have lost their lives due to rain-related incidents since the beginning of monsoon.