I had a 9 month gyp wouldnt cross water for nothin, so i found a deep ditch (up to my waist) carried her in and dunked her. Let her run/swim out then pulled her back in with the 25' check cord i had hooked to her collar.. shes still not real fond of water but for a pig or me shell get wet. Did take a couple hours though. She just needed to learn she could do it. Not sayin it will work for you but thats what i did.
Thats kind of the idea i had in mind next.... either that or taking him to the lake and throwing him out of the boat and letting him swim for a little bit....
I would leave him behind if your comfortable doing so. Give him time he will figure out that he will have to get in the water or get left behind.
I tried that, but he will just sit there or run alittle ways up and down the creek....
But #1, If i leave him for a good distance and have to walk back to get him, i will be twice as mad for having to go back,
And # 2, im not too comfortable leaving that much moneys worth of dog and equipment out in the woods...