Saludos!
Eco Tours located in Paraiso has a tour to Lago Enriquillo. Their phone number is 809-243-1190. They have a website too at
Eco-Tour Barahona - Our ecologic trek : the coffee trail - Charco Blanco.
I did the tour with them this past July-you can see my photos here at DR1 at
http://www.dr1.com/media/showgallery.php/cat/505 and my trip report at
Southwest Barohuco, Lago Enriquillo, Bahia de Las Aguilas.
Let me know if you have any more questions.
Paul