According to this page "The Otter's Holt" was written by Martin Crehan. Other sources say it's by Junior Crehan.

A Dutch band called "Fling" has a very nice instrumental medley called "The Cat's Whiskers/Otter's Holt" on their album "The Blackbird" which you can find at their website here. (To play an mp3 sound sample, click here.) I recognize the tune as the same one that Andy M. Stewart used for his charming song "Take Her in Your Arms" -- which has nothing to do with otters.

Here's a tune that I copied from http://www.cnnw.net/~oneil/o.html#12

X:
T:Otter's Holt, The
T:Poll an Madra Uisce
S:irtrad-l, Ethan Hack, 10/94
D:Bothy Band: "Old Hag You Have Killed Me"
N:3rd tune in the "Music in the Glen" Set
N:In Bulmer and Sharpley as "the Aughdarra"
M:C|
K:Bm
fBBA FEFB|A2 FB ABde|fBBA FEFA|B2BA B2de|fBBA FEFB|A2FB ABde|f2af effe|
[1dBAF B2de:|
[2dBAF B3A|:d3f a2fa|bfaf effe|d3f a2fa|bfaf e2fe|d3f a2fa|bfaf efde|fBBA FEFA|
ABBA B3a:|

Sorry, I haven't found any evidence of any lyrics to go with this tune -- other than Stewart's