A Guide to Colorado's Salmonfly Hatch
By Chris Steinbeck
The salmonfly hatch in Colorado is a highly anticipated event among fly fishermen. It typically occurs in late spring or early summer, usually around the end of May through June, depending on the specific location and prevailing weather conditions. The hatch happens on several rivers in Colorado, but the salmonfly hatches on the Colorado River and the Gunnison River are the most famous. These rivers, with their rocky bottoms, riffles, and abundant insect life, provide ideal conditions for the salmonflies to thrive during their nymphal stage and emerge as adults.
SIZE
Salmonfly stoneflies, also known as Pteronarcys californica, are among the largest stoneflies found in North America. They typically range in size from one inch to over three inches in length as adults. Their large size makes them a substantial meal for trout and other fish, which is why they can trigger such intense feeding frenzies during their hatches.
LIFE CYCLE
Salmonfly nymphs, like other stoneflies, prefer highly oxygenated water with rocks, sticks and other structure. These nymphs will live for up to 3 years subsurface, and go through several molts in their nymph stage. You’ll typically find them under rocks and logs in the river, or clinging on the sides of them.
Like other stoneflies, the emergence process begins when mature nymphs leave the water and crawl onto nearby rocks, vegetation, logs, or other structure along the river. Once they’re out of water, they undergo their final molt shedding their exoskeletons to reveal their winged adult form. As the nymphs migrate towards the edges of the river, they become vulnerable to fish. These fish will often key in on the movement of the fly, so swinging out patterns like Pat’s Rubber Legs can be a deadly option.
After drying their wings, the adult salmonflies take flight and begin their brief adult stage. As an adult, they live for a few days up to a week with their main goal being to mate, lay eggs and continue the lifecycle. As adults, you’ll find them on willows, tree branches and other structure near the river’s edge. When these adults land on the river, trout often eat them without hesitation often resulting in a splashy rise.
