What Breed Is My Dog?

I was told she's a Pit Bull/Rotti, but she looks nothing like a Rottweiler! I was thinking maybe Lab? She's a rescue, so I have no background information on her!

She's 10 months old and 70 lbs. I can't keep her out of water and she has a whip tail! She is super smart when she wants to be, but incredibly hyper.