Choose colours prussian blue, raw sienna and neutral tint (or paynes grey which has a little more blue) very small amount of burnt sienna

beware the neutral tint will give a very strong dark colour

 negative river1    negative river2    negative river3

Horizon line is 1/3 down the composition. Mix lots of paint cobalt + a little paynes grey

Wet paper with clean water paint across top 1/3 of paper and allow paint to dribble down control the flow move your board around. There should be a white area. Dry. Turn board upside down and paint clean water along horizon line allow paint to dribble down adding some lighter green.

 

Turn board around and paint clean water into the white area at the front of the composition. Using the same colour as the sky allow paint to dribble down (board upside down!)

Paint in green in foreground. Dry

 

 

Paint in the darker trees in background with same blue / paynes grey mixture. Paint in trees on left with broad strokes downward - important leave some white spaces. Paint the negative shapes around the bush middle left. )it's easier to draw in the edges first.

 negative river4    negative river final    
Using a dark mixture of grey, blue and raw sienna add in the river with some white areas for reflections. Paint the negative shapes around the grasses (easier to draw in before painting). Paint lighter refections using vertical strokes at the bottom of the river foreground.   Using a dark green paint in the trees (top left) leaving some white areas. Add more darks to the trees in the backgroung. Add the green reflections in the river bottom right. Add some branches