Lake McDonald is a beautiful mountain lake at the west end of Going to the Sun Road in Glacier National Park. It's 10 miles long and about a mile wide.
Lake McDonald Lodge is located near the north end of the lake just off Going to the Sun Road. The small village of Apgar is located at the south end of the lake. Apgar campground and Fish Creek campground are nearby.
The lake tends to be calmer than St.Mary's Lake on the east side of the park, but is a mountain lake, so care should be taken.
Assuming a start at Apgar, paddling the perimeter of the lake offers stunning mountain views, opportunities for viewing wildlife, and, if you're so disposed, a stop at Lake McDonald Lodge for lunch.
Another option is paddling one way from Apgar to Lake McDonald Lodge and then taking the shuttle back to Apgar to pick up your vehicle. Crystal clear water and a relaxing paddle in the mountains are a bonus.
Apgar and Fish Creek campgrounds are both excellent. West Glacier has some accommodations, and Columbia Falls and other area towns have camping and motel choices.
Daily National Park fee, or Season Pass is required.
From St.Mary's, MT: the incredible Going to the Sun Road is the most scenic route. Plan on an hour and a half or so from St. Mary's to Apgar.
From West Glacier, MT, Apgar is just inside the park.
There is a lot of information on the internet for Glacier National Park. Lake McDonald as well.