I really like the Woodland Scenics Realistic Water (NOT water effects...that's more for moving water, not still water like a swamp).
You can find a video of a small diorama I did here:
http://www.youtube.com/watch?v=67gyfj0jJeY
It was a bit of a pain to figure out HOW to use the product, but after I got it, it worked quite well. To get the blue color in the water, but still let it be clear, I put several drops of
GW's Blue and Green inks as well as a small amount of the Realistic water to a paper cup. I mixed it up until the ink was well mixed into the product and then poured that into my diorama. It stayed a bit cloudy for 2 or 3 weeks, but once it cleared up completely, I could definately see that the water was bluish green and the underlying lake-bed was still a slight shade of the brown that I had drybrushed it before pouring the water into the diorama.
Hope that helps some.