I adopted a pound puppy several years ago also. She was very reluctant to have anything to do with the water at first but I knew she needed to love it or she'd be left behind alot when I sailed. I started with a small plastic child's pool with about 3 inches of water in it and would work
with her in it, trying to always make it fun...having balls and other toys...and giving her treats in and out of the water. She still does not like the surprise of stepping off shore into water with "no bottom", but she loves swimming, retrieving sticks, and sailing. In fact, she now hides in the cabin
when she sees me packing up at the end of a weekend on board...anything to keep from leaving the lake.
Good luck and don't give up on your dog...yet!