The Finisk is a small tributary flowing into the Blackwater close to Dromana.
Charles Smith wrote of it in 1774:
There are several other lesser rivers in this county, as the Finisk, which rises near the north west bounds of the county, at Ballynamult; and, after a course of six or seven miles, empties itself into the Blackwater, to the north of Dromana.
That was in the context of a proposal, revived in the nineteenth century, to link the Blackwater to Dungarvan via the Finisk and Brickey rivers. Despite what some folk believe, I don’t think the proposal was ever carried out; you can read my conclusions here.