Marsh Landscape by Stanisław Mastowski, watercolor, roughly 6 x 18″ (15 x 46 cm), in the collection of the National Museum in Cracow, Poland.
The link is to the image page on Wikimedia Commons, from which you can access the large version of the image. I recommend it; the crops I’ve shown here don’t give an adequate feeling for the scope of the painting.
In the large version of the image, we can also see the artist has used two pieces of paper put together to accomplish the desired proportion.
In this seemingly simple scene of a flat march landscape, Mastowski has extended the normal range of composition into a immersive panorama, enlivened with contrasting bands of light and dark value, and subtle color shifts pulling us back into the distant row of trees. Notice how simple and direct his shapes are.
The feeling of light on the water is just wonderful.