Simulating water has always been a challenge for me. Modelers use a number of methods and I've tried several of them with mixed results. I had tied the 2-part resin method on an earlier module but was unhappy with that result. It had absorbed some of the surrounding color and I could not get the small bubbles out before it hardened.
Then on a home layout I tried Woodland Scenic realistic water after painting the bottom surfaces with blended green, blue, and brown acrylic paints. This had better results on flat surfaces but I was not really happy with the effect of water running down hill.
Using a scrap of Plexiglas, I experimented with both these products to seen how they would interact with each other and with acrylic paints. Also I wanted to practice working with this technique before actually applying it to the module.
Prior to adding the simulated water, I added some more rocks to the river bed. From some coarse sand I selected grains that were more rounded like rocks in a river bed normally are. I probably could have added many more than I did but put enough in to get the effect I wanted.
I put down 1 layer of the gloss medium and let that dry. Then I went over the deeper areas with a very dilute mixture of green and blue acrylic paints. After the acrylic paint had dried, I added another coat of gloss medium.
Of the methods I've tried for modeling water I like this one the best, particularly for running water. It's not the fastest but seems to offer the most control.