Explaining Northern California’s Legendary Hexagenia Hatch

If every ardent fisherperson in Northern California went fishing at the same time, think of how clear the freeways might be! Restaurants and grocery stores would seem like morgues, and distant parking areas along famous fishing venues would resemble a Costco parking lot on a Sunday afternoon. 

NorCal is justifiably famous for good fishing. But even so, there are particular times and places where fly fishers turn into zombies, obsessively flinging dry flies the size of small birds in the inky blackness of night. It’s all about special bugs.

Called “hatches,” there’s a big one in the fall (the October Caddis) and another happening right now (June-July), the legendary “Hex hatch” on Fall River and Lake Almanor. Hex is short for Hexagenia limbata, a giant yellow mayfly that swims up from the bottom of muddy lakes and streams once each year popping out of the water and thus becoming huge targets for hungry fish. The big Hexs cannot live just anywhere, but every state except Alaska and Arizona have Hexs. Such a big mouthful is capable of whipping the fish into a feeding frenzy. And the fish aren’t the only ones rising to the occasion.

The anglers attracted to this outrageous fishing are almost as obsessed as the fish. Under cover of darkness a flotilla of boats move out onto the waters while there is still some light to see, anchoring up in spots that have been good to them in the past. Some nights there is a good hatch, while other nights it might be slim pickins. When the hatch is on, the big bugs start appearing right about when you can’t see your hand in front of your face. On a good night the feeding can sound like it’s raining bowling balls. 

On Fall River north and west of Fall River Mills, the hatch is best in the lower river. Lake Almanor is next to the town of Chester in Plumas County, and the big bugs prefer the muddy west side of the lake. The procedure is much the same at both locations, except that Fall River is slowly moving water while Lake Almanor is still.

It’s often best to arrive an hour or so before dark. Before the bugs start hatching on the surface they have to swim up from the bottom, so that’s where the fish will be hunting them. Anglers often start by fishing a Hex nymph pattern on sinking fly lines. On Fall River that means making a cast from an anchored boat and either let the current slowly move your fly or initiate a slow retrieve. On Almanor anglers make a cast and then slowly troll from float tubes, pontoon boats or prams. Don’t worry about missing strikes. The fish often crush a slowly moving Hex nymph.

When the bugs start appearing on the surface it’s time to switch to floating lines and big dry flies. If there is any light at all, you can see the strikes and react accordingly. Fish will keep feeding well after we can see the strikes putting anglers in an unusual position. Instead of seeing the strikes and reacting, you have to rely on hearing the strikes and setting the hook. It won’t always be your fly the fish was taking, but when it is, you will know for sure! Both Fall River and Lake Almanor can grow huge rainbow and brown trout. On Almanor you might also tie into a smallmouth bass. 

If you haven’t tried this quirky, zombie summer night fishing, perhaps it’s high time you did. Google NorCal Hex fishing guides for a long list of pros who can hook you up

Chip O'Brien

Chip O'Brien is a regular contributor to California Fly Fisher and Northwest Fly Fishing magazines, and author of River Journal, Sacramento River and California's Best Fly Fishing: Premier Streams and Rivers from Northern California to the Eastern Sierra. He lived in Redding, California, for eighteen years, where he was a guide, teacher, and regional manager for CalTrout.

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