I know VERY little about the movie, which is making it so difficult to find it.

It was animated with a bunch of different kinds of animals.
It was very hot and there was a drought.
Something happened and they found or built an oasis.
They were swimming, playing a waterfall, relaxing.
Then something bad happened... <insert villain here>.

I don't really remember anything else. I can picture it in my head, but it's been so long ago and I think I only saw it once on TV.

Does any of this ring a bell for anyone?

Land Before Time? Maybe. Dinosaurs on trek to find the last fertile land. When they do they swim, play, etc...

No, Land before Time was in the 90's. Will try and think of it for you.

You are prob correct that this is not LBT, however it was first released in 1988.