Streams and rocks are typical subjects in landscape painting. They both require a bit of blending for realistic results, a task made difficult in acrylic painting because of the fast drying time. Mix the acrylic paint with water to slow the drying time and make the blending of colors easier.
You know what a stream looks like, but for the most realistic and visually interesting results, choose a photograph from which to paint. A richer experience would be painting a stream on location, but this can be problematic. If you choose to paint a stream on-site, bring as few tools as possible so you can pack up quickly if necessary. Take into account the wind and possible precipitation.
Start painting the stream with a medium-sized brush. Lay down a wash of paint for the base color, either blue-brown or green-brown--streams are rarely blue. While the base color is drying on the canvas, mix some white paint on the palette with a portion of the paint that you used as the base coat. Switch to a slightly smaller brush. Dip the brush in a jar of water and then in the paint, mixing the two together.
Paint a wash of the watery paint over the foundation already laid down for the stream. Allow the darker color to show through the lighter color. Switch back to the darker color on the palette to paint ripples in the stream.
Mix gray and brown paint on your palette with a medium-sized round brush, then paint the irregular shapes of rocks in the stream. Darken 1/2 of the mixed paint by adding more dark brown. Dip a smaller brush in the darker brown paint and use it to shade the bottom 1/2 of the rocks.
Mix white in the other half of the rock-colored paint on the palette. Dip a thin paintbrush in the lighter color and paint the light glistening on the top of the rocks. Dip your brush in the darker color and give shape to the irregular surface of the rocks by painting the dips in the surface as shadows.
Integrate the rocks with the stream by painting the flowing water around the rocks. Dip a thin brush into the darker color of the water on the palette, then paint that color around the tops and sides of the rocks. Garnish the flowing water with white paint to show the light reflecting off the stream.