It looks like Boxers are different when it comes to water. My old Boxer from years ago, used to love the local pond near my house. He wouldn't swim as such, but bounce on his back legs on the bottom of the pond. But he certainly wasn't scared of the water. Apart from one time, an idiot some how managed to throw a wooden picnic table into the middle of the pond, the top just showed over the surface of the water. So, Sammy bounced out to it and climbed aboard. Unfortunalty he got stuck, he didn't have the guts to jump off and back into the water, after trying everything I knew to get him back, I had to wade out to him and carry back. Sometimes they are too clever for their own good.
My puppy Boxer is very unsure of water right now though. I took him and my mutt to Barton Spring in Austin for a day out. This is a cool place where you can go swimming with your dogs in the spring or the river. My mutt just jumped straight in but I had carry little Winston out to the deeper part. I held him underneath, and he tried to doggy paddle. As soon as I took my hands away he sunk!!!! But, know he is getting better, especially down our dog park. The problem with Texas in the summer it is soooooo hot. Winston just goes and stands in the pond upto his chest and doesn't move. So, hopefully this will get him more and more used to the water.