Amed is usually good for snorkeling during the dry season, particularly in front of Vienna Beach Hotel, but I've heard it's not so good in the wet season.
I've just got this off a website and I think this may sum things up:
"When it rains in the mountains above Amed, earth is swept into streams and brought into sea which thus turns brown and doesn't clear for several days. If you are happy spending days at the hotel pool, rain would probably not be that much of a problem as it could be for snorkelers and divers."