Grass snake spotted today

For only the second time I saw a grass snake swimming in the moat. I was watching the ducks around mid day when I heard a little splash and saw a snake plop into the water about two metres away. They swim brilliantly - a very sinuous movement. It was about 400mm to 500mm long and surprisingly thin. The much fatter snake that I saw part of, a while back ,must have been pretty long if the proportions stay the same.