Be careful at El Valle
All this is true and the drive through the river is quite fun - there is a beautiful cascade to be seen on the main river, just drive onto the left along the river, or leave your car and walk, it is worth seeing. El vale beach is wonderful , and a river of fresh water comes out of a small cave, it is great.
BUT be EXTREMELY CAREFUL when the sea is going down, the current is very strong, and there are often people drown. Just enjoy it but keep in mind the danger.
Just to make you smile : there is a guy of the "marina " on charge of looking at the security. When asked "what do you do if someone is having problems ?" the answer was " I call the marina in Samana and they come with a boat".... Of course there are also fishermen who could help you , but better avoid any risk. When the sea is going up you can enjoy the water without problems.