recommendations for open water training

Hi Everyone:
I registered for the swim and have been training in a pool since September. I am very excited about the swim.  My question is: As I have never done any significant swimming outside of a pool, I would like to try some longish swims in lakes this summer before the big day.  Does anyone have any suggestions?  We own a kayak and my wife would paddle next to me so I am not concerned about safety but I would like some place reasonably free of heavy boat traffic where I could swim unmolested.

Thanks!

Josh