In theory, fly-fishing is a simple sport: Pick a body of water, choose a fly-fishing rod, select your “fly” (or bait), tie a secure knot, cast your line and, hopefully, land a fish on the other end.

The amount of new fly anglers entering the river in the past year has been astounding. Urbanites across Colorado are heading to the mountains for a much needed COVID-19 escape. Even locals who have ...