Had a lab pup that wouldn't have anything to do with going into water. She had a little troll doll (see, this was a long time ago)that she carried by the hair incessantly. She never marked it or chewed on it.

I took her down to a pond which had a really gentle slope to it, and pitched her "baby" into the pond just out of her reach. She paced up and down the sand barking and whining, looking for all the world like a distraught Mama. All the while, I was telling her, "C'mon, lets go get it!" Finally, I stepped into the water, and she put her forelegs in, just enough to save the baby. I praised her and petted her while she held the baby for a while, then I tossed it a little farther. We probably did only about three times or so that first day, but each toss, she went in just a little farther. It worked for us.

This was a really timid dog. She did not like gunfire either, but I worked her thru that as well. However, I was never able to get her to trust people. When we would be hunting dove, and someone would stop to visit, she would invariable sneak off and hide in the brush until they left. Exasperating! Bird hunting, in my book, anyway, is a social event.

How long have you had the pup? When did you first try to introduce it to water? Has the dog had any prior bad experiences with water?

You could try bringing another dog that likes water to see if your will join in on the fun.

Also you could try getting a wing clipped duck and have them chase it.

Is this pup from hunting lines or just a pet? The pup is more than old enough to be introduced to water.

Have you tried going somewhere and actually get in the lake and play with kids / family / friends and see if it gets him excited? Not just wade out, I'm talking like a play day at the lake where everyone is splashing around and playing about 20 - 30 feet out from the bank.