Upper Waterton Lake
The townsite of Waterton is adjacent to Upper Waterton Lake. The lake stretched roughly north-south for about 11km and a boat trip can take you south to the American side.
Emerald Bay (on the northwest corner of the lake) offers the easiest paddling with pea-gravel beaches around the western perimeter and shelter from the wind. There is decent parking and washrooms here. There were deer in the picnic area here.
We had a nice time for about an hour checking out the marina, the breakwater, and the bay. The place was packed by the afternoon with boaters and swimmers (although at 4C, I thought the swimmers were brave).
There is also access to the lake all along the eastern and southern edge of the townsite. The beach isn't as nice and you must contend with the wind and the waves right away. The very south end of town (past the campsite) looks like a decent spot to launch from if you wanted to go down the lake a ways.
To the east of Emerald Bay is the narrows that separates Upper and Middle Waterton Lakes (on my map it is shown as the Bosporus). I wanted to get over here but the wind came up and I didn't want to try cutting across two-foot rollers with Jessica (who is a slow paddler). It is also possible to access the narrows from Middle Waterton Lake.
Middle Waterton Lake
You can access the lake from Driftwood Beach (parking lot, boat launch, picnic site, washrooms) right across from the Parks Operations Centre. This lot also gives you access to Linnet Lake (see below). You can also access the lake from a parking lot a few hundred metres further towards the park gates.
You can paddle from here around the headlands and access the narrows from the north side. We saw a bear and two cubs swimming in the narrows while we were there.
Lower Watertown Lake is the closest lake to the park gates. It connects to Middle Waterton Lake through a small creek called (rather dramatically) The Dardanelles. We did not try this connection.
The best access is at the northern tip of the lake at the Knight picnic site. A very short carry from the parking lot to the rocky shore gets you on the lake.
The lake also connects at the north end to Maskinoge Lake and, via a river, onto the Waterton Reservoir (we did not paddle either of these lakes).
The last lake we looked at in the park is tiny Linnet Lake, located just north of the Prince of Wales hotel and accessed from the Driftwood Beach parking lot.
The lake is small and entirely sheltered. It would be a great paddle for kids.
The lake was, however, signed for swimmer's itch. It was also just a nice sheltered place to read a book out of the (relentless) wind.