Re: RMNP first timer
Cub Lake Trailhead to Fern is listed at 5 miles. I walked about 4.5 before I started fishing. Great hike and you pass near the Big T. headwaters and a couple of other nice small streams as alternates.
If you do go to Bear Lake consider hiking to Dream Lake. It's a mildly steep 1.1 mile hike but there are big greenbacks in that little lake. The water is often crystal clear and you can watch a big trout lift off the bottom and sip an ant off the surface. That trail is often crowded with hikers but when I've done that trip I've been the only angler so I just had to put up with hoofers along the edge of the lake.
I also like Sprague Lake. It's easy access so it can get crowded but there are several little feeder creeks with beaver ponds and, if the water isn't raging, Glacier Creek is nearby.