Northeast of Denver near Estes Park, the Big Thompson River (aka Big T) is a surprising large river for the Front Range. The upper Big Thompson River starts near Moraine Park in the Rocky Mountain National Park and flows east through Estes Park and down into Lake Estes. The river combines with water diverted from the western slope before heading out of Lake Estes. The lower Big Thompson below the Lake Estes dam is an atypical tailwater fishery that heads quickly down a rocky canyon east towards Loveland. Due to its rapid descent, it get opaque and warm quickly. If you can find the right pockets among the big boulders, you will find some very large rainbow trout and brown trout.
Note: The printable fly fishing river map is provided courtesy of HANDYMICROFIBERCLOTH.COM.
Overall, Big Thompson River - Lower is the 30th most popular fly fishing river of all 47 fly fishing spots in Colorado.