If you don't have the score (free): http://imslp.org/wiki/Etudes,_Op.25_%28Chopin,_Fr%C3%A9d%C3%A9ric%29
I prepared my own free PDF of the score with the bass melody notes highlighted. https://drive.google.com/file/d/0Bzwr-5tDUtSEVGZwOFJRek85QWM/view?usp=sharing
If you're interested in a video link, here's an old family video of a trip across a choppy sea on a stormy day in a small boat to Maya Bay in Thailand (setting of The Beach) The colour of the sea on our journey turns from grey, to black then the clearest emerald green in the lagoons.
Content ID please note: This video is played by Paul Barton, the channel holder, of a musical work in the public domain and NOT owned by Music Publishing Rights Collecting Society as currently claimed and consistently claimed on my videos.