Local legend says it was named after a woman named Roksanda, but that is lay etymology ( Rusanda and Roksanda are pronounced a bit similarly, probably because of that the legends came up with this explanation).
Given when the first mentions in written records of this toponym appear, the name of the lake Rusanda was derived from a praslavic root word and meaning of it has to do with colour red as in hair colour - ginger.
***
"Rodoslovlje" Serbian Genealogy Society
www.rodoslovlje.com