I was in San Sal about a year ago, I was not a diver at that time. We did a lot of snorkeling around the island and it was clean of things I'd have considered trash. (not knocking your hobby I'd just not considered that to be something to look for until today) There are several wrecks though around the island. There is a dive shop there which can give you a map which shows them. Some of them are pretty old so maybe there is a chance you'd find something good. Great island we loved our time there a lot. Paridis Restaurant up near the airport is excellent and you just cant miss eating there. Grouper fingers, conch fritters, ribs, mutton, and so much more is offered there. Each day check the daily board for specials. We ate there everyday for about 10 days and it was a highlight of the day.