nadyāḥ kadācid āgatya
tīre nikṣipya pūrva-vat
vāsāḿsi kṛṣṇaḿ gāyantyo
vijahruḥ salile mudā
nadyah -- of the river; kadacit -- once; agatya -- coming; tire -- to the shore; nikshipya -- throwing down; purva-vat -- as previously; vasamsi -- their clothing; krishnam -- about Krishna; gayantyah -- singing; vijahruh -- they played; salile -- in the water; muda -- with pleasure.
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 Vrishabhanu 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 avabhritha-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 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 take bath 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 Krishna to become their husband, and Krishna wanted to fulfill their desires."