You'll start your loop around Mountain Lake with a short jaunt to the boat launch. This is a delightful, quiet spot when the lake is shrouded in fog, but it is quite scenic in sunlight, too. Turn north from the boat launch, following the trail as it stays close to the lakeshore. On your left are tall trees that house various birds; be sure to bring your binoculars!
Fishing birds like osprey, kingfishers, heron and ducks hunt here, while the rat-tat-tat of woodpeckers resounds in the forest. After a little more than a mile, you will arrive at a junction, where you'll turn right.
The flat trail along the shoreline continues, interrupted only by a climb up a small ledge. After hiking 3.75 miles, you'll arrive at the south end of the lake, where you can examine a small dam and take a rest. If the day is clear, you can see Mount Constitution, complete with the tower on top of here. Be sure to stop and take a few photos.
Pressing on, you'll cross Cascade Creek on a bridge. There is a side trail here that leads to Mount Pickett — you'll want to avoid that one in order to complete your loop. The trail to Mount Pickett is enjoyable, though, and worth venturing down if you have the time or inclination. Just be aware that there is more elevation gain than your flat route around Mountain Lake.
Past the creek, another trail branches left. You'll avoid this one as well, instead staying close to the quiet shoreline along Mountain Lake. Keep your eye out for more wildlife, and soon complete your loop hike.