This is "Alders" by Charles-François Daubigny. Painted in the French landscape tradition, it's a serene evening scene depicting Daubigny's home in Auvers-sur-Oise. The surface of the water is covered with vegetation and reflected light from trees and bushes. A woman sits at the far side, under a clump of alders, wearing a red and white hat.
The painting features a range of painterly techniques, including wet-in-wet application and textured surfaces created by short parallel lines. In some areas, these lines may have been made with a graining comb. The artist has also captured the sense of impending dusk with the mauve colour of the clouds on the left side of the painting.
It's worth noting that this is one of several compositions painted by Daubigny in 1873, all depicting views from his home in Auvers-sur-Oise. While they share similarities, each has its own unique qualities and treatments of light and atmosphere.
Alders hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.