From Steve Schweitzer's A Fly Fishing Guide To Rocky Mountain National Park, flyfishingrmnp.com:
Prospect Canyon to Glacier Falls:
The lower section of this stream gets plenty of fishing pressure since it is nearly drive-by fishing (follows Bear Lake Road) however, it fishes well for brookies and rainbows. Consider taking a walk up to Mills Lake ...
Getting there: From the Beaver Meadows Entrance, follow Bear Lake Road to the Beirstadt Lake Parking Area or the Glacier Gorge Parking Area. The creek runs east and south of Bear Lake Road and can be accessed from Glacier Creek Trail from the Glacier Gorge Trailhead.