blutooth-
Some of it will have to do with how well your dog behaves in public. Mine are getting there, but I still do not feel like they are ready to go to a beach where there will be others in close proximity or heaven forbid another dog within eyesight. Not that Huck or Millie would bring any harm, but can sure be overwhelming with their greetings.
Anyway, if your dog is well behaved around other persons and dogs, then just about anywhere. I would think that you could even find a stretch of beach at McLain that it would be alright to let it swim. Otherwise just up the road a bit is Calumet Water Works park and there are usually spots on it that you can go and be alone. Eagle River is a good one during the week- especially when the weather is not really good beach weather, otherwise you will usually encounter persons. Between Eagle River and Eagle Harbor is Great Sand Bay. Tons of space there, but on a good beach day, most of the spots where you can climb down from the road have folks at them. Just up the road from Great Sand Bay is Cat Harbor, usually pretty quiet there, even when others are busy. Not the best human beach, but my dogs love it there.
Good luck and have fun!
-John