There is plenty of parking at the trailhead and water is nearby in the Arapaho Bay Campground. First mile is a steep climb with no shade - bring lots of water.
Watanga Lake (10,772') is located about 4.5 miles (9-9.5 round trip) from the Roaring Fork Trailhead on the west side of the Indian Peaks Wilderness. The main lake is fairly small but set among broad, flat meadows that give it a larger and particularly spacious feel. There are a couple of smaller lakes in the upper valley southeast of the main lake. This makes for a good day run or short distance backpacking trip. The trail is mostly a Blue/Intermediate trail rating; however, the steep sections may challenge even very fit runners. I would not recommend this trail for kids under 10.
To access the trail, start on the Roaring Fork Trail # 3
. Roaring Fork Trail climbs very steeply in the first mile, then moderates along the creek to the Watanga Lake - Stone Lake fork, about 2.6 miles in. Go left at the fork for Watanga, or right for the Roaring Fork Trail # 3
and Stone Lake.
Most people won't go this far due to the steep start. Good for you! You just scored a trail to a lake with minimal people on the edge of Rocky Mountain National Park!
Past the fork, the trail gets progressively steeper and more open until you crest a small ridge and descend into the lake area valley. Enjoy the beautiful views!
I don't recommend running the first mile from the trailhead in the late afternoon as there is limited tree cover in this very steep section. It can be very hot in the summer! After the steep section, you enter a lush forest and run along the creek most of the way to the fork.