From Steve Schweitzer's A Fly Fishing Guide To Rocky Mountain National Park, flyfishingrmnp.com:
Three hundred yards to the north of Spruce Lake is this fast flowing creek. The creek has heavy overgrowth and plenty of streamside boulders which make following the creek slow going. The best way to ...
From the Beaver Meadows Entrance, take Bear Lake Road to Moraine Park Road to Fern Lake Road to the Fern Lake Trailhead. Take Fern Lake Trail to Spruce Lake Trail to the lake. The first 1.8 miles of the trail is deceivingly flat and easily traversed. It lulls the unsuspecting and unprepared into thinking the rest of the hike is similar. After 'The Pool', the off-trail hiking gets a bit steeper. Hiking from the trailhead to Fern Lake is about 4.2 miles one way. From Fern Lake, it's approximately eight tenths of a mile to Spruce Lake.
The best way to get there is to follow the outlet out of Spruce Lake, which brings you to the stream, but it is definitely rugged travel. The better fishing is well upstream (six tenths of a mile), but requires even more rugged travel to get there.
These waters found on or near the trail are considered barren: Cub Lake, lower and upper Spruce Creek, Marigold Pond, Marigold Lake, Two Rivers Lake, Primrose Pond, Round Pond, and Lake Helene.