Srimad Bhagavatam Canto 10, Chapter 22, Text 07

SB 10.22.7

nadyah kadacid agatya
 tire niksipya purva-vat
vasamsi krsnam gayantyo
 vijahruh salile muda
 
Translation: 
 
One day they came to the riverbank and, putting aside their clothing as they had done before, happily played in the water while singing the glories of Krsna.
 
Purport: 
 
According to Srila Visvanatha Cakravarti Thakura, this incident occurred on the day the young gopis completed their vow, which was a full-moon day. To celebrate the successful completion of their vow, the girls invited young Radharani — the daughter of Vrsabhanu and the special object of their affection — along with other important gopis, and brought them all to the river to bathe. Their playing in the water was meant to serve as the avabhrtha-snana, the ceremonial bath taken immediately upon the completion of a Vedic sacrifice.
 
Srila Prabhupada comments as follows: “It is an old system among Indian girls and women that when they take a bath in the river they place their garments on the bank and dip into the water completely naked. The portion of the river where the girls and women bathe was strictly prohibited to any male, and this is still the system. The Supreme Personality of Godhead, knowing the minds of the unmarried young gopis, awarded them their desired objective. They had prayed for Krsna to become their husband, and Krsna wanted to fulfill their desires.”
Srimad Bhagavatam Canto 10, Chapter 22, Text 06
Srimad Bhagavatam Canto 10, Chapter 22, Text 08