One tip/public service announcement/small rant. Please don't make your waterfalls blue.
Blue waterfall textures are a classic mistake most people make (probably because the default water textures in the library are blue). They make for very unrealistic "SL water", which no matter how commonly accepted, really looks quite terrible.
For much greater realism, keep your waterfall textures very pale, even white. It looks much better.
In RL, oceans and lakes often do tend to look blue. But when a river flows over a cliff to become a waterfall, it gets churned, broken into droplets, mixed with air, and becomes a frothy white.
And the change doesn't stop with just color. Another big mistake a lot of people make is they make their waterfalls way too smooth. They end up looking like vertical rivers, not at all like actual waterfalls. In RL, falling water is never smooth (except when coming from man-made fountains and faucets, which are "tuned" to make the water behave in very unnatural ways).
Standing or flowing water is one contiguous body, but falling water is not. It's rough and billowy, since it's made of millions of individual drops. So don't expect to be able to use the same kind of texture for a a waterfall that you use for pools and rivers, and have it look realistic. Good waterfalls require their own separate textures.
For an example of what I'm talking about, there's this quaint little waterfall located about 20 minutes from my RL house. Here are a few pictures:
Oh, did I say it was quaint and little? Whoops.
OK, here's one that actually is. This one actually is about five minutes from where I used to live. (Waterfalls are stalking me, I swear. Every place I go, there they are.)
In each picture you can see pretty much the same pattern. Regardless of size, all waterfalls exhibit the same behavior. The water is its normal color while it's horizontal (blue if it's very deep and open to the sky, like the Niagara River in the first two pics, or black if surrounded by black rock like at Buttermilk Creek in the third image), but as soon as it rounds the corner to start falling vertically, it always turns white.
If it's not too much to ask, I'd like to take this opportunity to declare war on blue waterfalls in SL. It's high time we improved this long-standing, grid-wide eyesore. If you have a blue waterfall, desaturate its textures to turn it white. If your neighbor has one, tell him you're going to turn your place into a loudnoxious, lagtastic, disgustingly gaudy, ad farm if he doesn't fix it. Those blue waterfalls have got to go!
End of rant.
