The three lakes of Killarney all mix into each other at the "meeting of the waters". The whole area is splendid and there are lovely walks that you can take.
The birdge on this picture is where the waters actually meet - even though I don't quite understand how you draw a border between two lakes if they flow into each other.
Now this is getting a bit far to really qualify under Killarney. Even so, it's quite possible to make a quick drive over from Killarnaye and see Ladies View where you have a splendid view over the lakes of Killarney and the meeting of the waters.
If you'll be driving around the Ring of Kerry you will be driving past this spot anyway.