A great method for making brown water is to use ENVIROTEX Lite polyurethane resin. First prepare your base by building a dam around the edges to hold the resin inside. I used black sheet styrene and attached it to the base with super glue. I like to paint the "river bottom" using Model Master Dark Tan (FS30219), which matches the color of the Mekong River perfectly!
The next step is to combine equal parts of resin and hardener with a few drops of Dark Tan paint then mix the messy concoction together for 2 minuets. I like to pour two layers of resin to show depth so the first layer will be a little darker than the top layer. After the first layer dried completely pour the second layer and once its just about to cure use a wooden stick to form all of the waves.
After the waves dried I used Zinc Titanium White oil paint to make the "white caps" on the waves.
And presto, you end up with realistic looking brown water!
When the resin is still semi-wet you can add items like trash, leaves and various debris floating in the water. I added a clear empty coke bottle to this Zippo diorama...can you find it?
Another cool trick is to use household spackle to make the engine froth. You can either add the spackle before you pour the resin as I did with the ASPB above or add the spackle on top of the resin as here in this Zippo diorama.
The waves add realistic action to your diorama.
Close up of the spackle I used to simulate engine froth in this Zippo diorama. Notice the white oil paint around he edges of the spackle to blend it into the water.
The bow of your boat should have white caps unless you plan to display your boat in a static water scene.
Pouring two layers will achieve depth to your scene and you can see the side of the boat through the dried resin.
To give your water surface detail you can use clear silicone caulking. The first step is to open the tube and squeeze a sufficient amount onto the dried Envirotex surface. Wet your finger and spread the caulking around making small waves as you go. Make sure you only use a thin layer or the caulking might not dry completely clear.
After you allow the caulking to dry for at least 24 hours, paint the water surface with clear gloss acrylic paint.