Chaweng Beach was once very beautiful, but after over 30 years of unchecked building, littering, and sewage, it is now only a shadow of it's former self. The sea is dirty, and the reef just offshore has been devoid of sea life for many years, and many of the trees removed to make way for the hotels. The white sand now polluted with tiny bits of charcoal from countless fires.
The southern end is a little cleaner, due to there being no reef at that end, so the waves clean it more.
i often think the authorities should import one of those sand cleaning machines they use in the South of France, and give it a good wash and filter.
i can clearly remember being amazed at the beauty on my first visit back in the early '90's, and being warned to be careful of Stonefish in the sand in the shallow waters inside the reef. I doubt anything living there now.
Pattaya beach, Koh Lipe was another that was way up there in the beauty stakes, far better than Lamai in my opinion, but that also has been over developed.