On a recent trip to Acadia/Mt. Desert Island, the family went paddling on two lakes, Eagle Lake and Echo Lake. Our main boat for both trips was an Ocean Kayak Malibu II XL, can't say enough good things about this boat.
Echo Lake was a nice lake to paddle, not very big and some good scenery, despite the fact that part of it is not within the park and was studded with camps and cabins. However, for me, Eagle Lake is the main show in the park. This lake is pretty big and completely in the park, with unspoiled vistas pretty much anywhere you look.
We took a look at Jordan Pond (which is a big pond), but did not get a chance to put a boat in it. My vote is for Eagle Lake if you only have time for one lake paddle. As mentioned in a previous report, the lake got its name for a reason. We saw a couple of eagles working the water for fish, and there was a good amount of other wildlife about.
The lake is crystal clear and COLD, although no swimming is allowed (you can swim at Echo Lake, but you would have to be pretty darn hardy). As mentioned by others, if it is breezy, the lake can get a bit choppy, but nothing that should be a problem, especially if you stick close to shore. We combined our paddle with a bike ride around the lake, a perfect combination.
There were lots of opportunities to get out on the ocean in the area, and according to everyone I talked to the views were marvelous and the tides not a real problem. However, everyone mentioned the care needed to avoid the many rock outcroppings that characterize the coast in the entire area.
In short, if lake or ocean paddling are your thing, Acadia and the surrounding area offer you everything you could want (there is gnarly whitewater on the mainland too, but those days are behind me). If you take advantage of the hiking while you are there, in most areas in July and August there are tons of wild blueberries, we picked and ate until we were stuffed.
If you prefer to rent kayaks, there are plenty of places to do so on the island. All the rentals for ocean/sea kayaks seemed to be as part of guided tours, which were a little pricey.
There are many ways to stay near Acadia, from rustic camping to luxury resorts. We chose to stay in a little cottage near Bar Harbor, there are many of these in the area. Pick what works for you, the cottage we stayed in had a nice porch and a kitchenette, just the ticket for us.