There was an article in MR way way back about making lily pads and pond scum. Also way back, how to make cattails. Both were for HO, but maybe you can use the techniques. \
The trick with "poured" water is how to get it completely level. I don't think anybody's come up with the perfect method. For my flat, still water scenes I use thin clear styrene sheets, cut to fit the waterway, and light green coloring on the underside for that murky look. Thinned paint or Magic markers are good. If you don't overdo the coloring you can see the bottom of the pond like looking through water.