Golden Gel Mediums will offer you a variety of ways to get the finish and texture you want.
http://www.goldenpaints.com/products/medsadds/gels/gels.php There are other names available but this is the one I happen to use in fine art. They can be added to your pigment and upon curing give the end result. There are some that produce a sort of concrete/pavement texture, another that would create a dried mud surface with cracks, but for you, I would recommend creating the colour surface with the greens and browns you want then mix up a batch of the highgloss medium with a bit of the pigments you'd like to bring up a bit like algae or mosses floating in the water.
I know that there are specific products for modeling water effects but you're not wanting waves or rapids since it's a pitch showing markings if I understood correctly. You could, in fact, lay out a grid with moss, creepers and vines on your initial colour level then cover that with the gloss medium.
Remember that the most important visual aspect will be vanishing depth. Most of our light is reflected off the top of the water when we look in. Much of this pitch should look quite black with only areas of reflection, foliage, fauna, flotsam and jetsam for interest.
In the land of Pre-digital I had swamp terrain which looked quite good with no clear elements at all, just black and greens. The green was a glossy, metallic that had separated so I dabbed off the top carefully avoiding the metallic. A hint of green with glossiness. I've since given the whole set away.
Have fun.