I went to Juan Dolio. In the media gallery here on page 8 in the middle I have posted two pictures of the beach at the Coral Hilton in Juan Dolio. Although one just shows an iguana in the water...you get an idea how dirty the sand is( or isnt) some beaches the water turns turbid when the waves crash and it takes a while before the sediment settles...in good beaches there is no turbidity at all....like Sosua is the best that i have seen...the juan dolio beach wasnt bad....its not a deep beach,.....ie there isnt a lot of beach from the hotels concrete structure to the water......playa dorado has deeper beaches as does Sosua...dont know about punta cana, or la romana.
good luck
ps I didnt like the Coral Hilton. had a few issues and problems.....you may get luckier
bob