I’m guessing you already know this has been slightly doctored. The best part of the image for me is the 50/50 split between light and dark with the canal forming a river of light that the narrow boats are gliding along through a sea of black. The picture was actually taken at midday which helped create the final result. With the sun high above the over hanging trees on the left of the canal formed a deep shadow whilst the sun reflected brightly on the water. On the right of the image the canal path (just visible top right) held the trees back from the water and aided the composition. To get the final image you see here I simply used a high contrast black and white filter after manually using the exposure brush to deepen the shadows and burn out the water.
Taken near Stockley Park, London on June 28th 2012