Ao Nang Beach is a lovely beach for walking, but not a great beach for swimming. At the beginning and end, rivers flow into the sea, obviously carrying untreated water, and the beach water is also quite murky. It is better to take one of the many boats over to Railei Beach and go into the clean water there. A walk along the beach at low tide is beautiful, though. At high tide, the beach is partially submerged, but you can then walk along the beach promenade above, which is also the alternative on the way there and back. At low tide, you can find a surprising number of mussels and snail shells, although the beach is quite busy. If you are too KO for the way back, you can take one of the many tuk tuks back. Just speak to the drivers and the prices seemed OK to me.