Well, Kellswater was also recorded from Paddy Gamble of Ballymoney, Antrim, and appeared on the LP Killeavy's Pride.

I was also going to riposte that Steve Roud's Folksong Index, lists 16 sources for this song. However:

The Index assigns Kellswater the number 916. Of these, 11 are Canadian, 2 are from England, and only 3 are Irish; Gamble, Carmichael, and a Donegal version from Herbert Hughes' Irish Country Songs.

What's confusing me is that I've just had a look in Maud Karpeles Folk Songs From Newfoundland at one of these sources. The song in question is called called ON BOARD THE GALLEE and seems to have no connection at all with Kellswater. It is in fact a ballad, roughly along the lines of John Reilly (the one which has "Oh father dear don't be severe to send my love to sea"). Moreover, the titles of the other non-Irish versions are; In Bristol City There Lived a Fair Maiden, Jimmy and I Will Get Married, Lovely Jimmy, A Rich Merchant in London, Shot Like a Bird on the Tree, and Oh in Leinster There Lived a Youg Damsel.

It rather looks as though Roud has included two different songs under the one number and that Jim Carmicael's Kellswater is indeed a fairly uncommon song.