I would beef up the deck, somewhat, with maybe double joists. The water at
3 foot deep will weigh in at about 25 pounds per square foot, and though the
standard floor joist design is for 40 or 50 pounds per square foot, most
don't have anywhere near that. When people put a hot tub on the deck, they
usually add some support, and it is about the same dimensions. You could
also add insulation under the liner and around the sides to help keep the
pond from freezing quite as quick. Without the ground level heat, I would
suspect it will freeze deeper than most ponds.
--
RichToyBox
http://www.geocities.com/richtoybox/pondintro.html

"Derek Broughton" wrote in message
...
I'm going to be building a pond on my new deck this summer. It'll
(probably) be about 8' x 3' x 3' deep.
It may be a little shallower, but not much, because I really think you
need
that deep for lilies (I know you can grow them in less - my first was a
dwarf in a tub - but you should see the lilies in the 5' deep part of my
second pond). It could be a little wider too. It will be a formal pond,
and I'm thinking of building it with vertical wood sides (lined), and
hanging planters off the side (like window boxes - but inside the pond)
for
shallower plants.

Has anyone else done something like this? Is there anything in particular
to watch out for? Freeze thaw cycles could be hard on it (and my deck) if
it isn't done right.
--
derek