I would work them out slowly into the water making it a great fun experience. Also try getting in the water w/ your dog. Here is you standing on land telling them to jump in to something they are unsure of. If you get out there and make it lots of fun they should be willing to come out after you. (The first time I did this I came out bleeding from the scratches so be careful)
Maybe think about getting a new toy (that floats) that your dog is crazy about. Associate that toy w/ going in the water and it should help. We have a "chuck it" that we only use at the lake and the dogs know when it goes in the water they go and get it. It is a bit of a competition to see who can get if first (always Shelby but Jackson keeps trying).
Just keep it up, and make it fun and soon you will have a hard time keeping your dog out of the water
