SB 1.13.52
srotobhih saptabhir ya vai
svardhuni saptadha vyadhat
saptanam pritaye nana
sapta-srotah pracaksate
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The place is called Saptasrota [“divided by seven”] because there the waters of the sacred Ganges were divided into seven branches. This was done for the satisfaction of the seven great rsis.