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The Henry’s Fork in August & September: Fly Fishing Prospects Look Excellent

Jul 29, 2010

August and the first part of September still qualify as summer in our part of Idaho and Montana. Much of the Henry’s Fork fishing slows down, but the patient dry fly angler can stalk the Harriman State Park water or fish near the Lodge – and still find fish rising to good hatches virtually every day.

Of special note are the cinnamon ant flights of July and August.

When the cinnamon ants fly (in mid to late August), our normally picky rainbows abandon all caution and become ravenous eaters.



A Henry’s Fork Rainbow (image Ron and Anne Gadberry)




Fish that wouldn’t move asix inches to eat your dry fly will move 3’ or more to take a flying cinnamon ant, which is usually a size 14 or even bigger (see our prior article for more information about the cinnamon ants).

On the Ranch or near the Lodge, you will find plenty of big rising fish.

Three other waters that come into their prime during the August/September period are the South Fork of the Snake, the Madison and Hegben Lake.

Hebgen Lake

Hebgen Lake is home of the famed “gulpers” – large rainbows & browns that rise to dries in a beautiful, placid morning setting. You will almost certainly see 16-20” fish cruising for mayflies in the morning.

The trick is to place your dry fly about 5’ in front of a moving, rising fish. Hebgen is one of the guides’ favorites in August and September.

When the afternoon breezes come up, your guide can take you to another great spot; a morning on Hebgen and a float down the Madison or Box Canyon of the Henry’s Fork is a fabulous combination!

Nearby Quake Lake has similar fishing and August brings hatches of spruce moths that can make even the big fish lose all their caution.

South Fork of the Snake

The Henry’s Fork’s big brother is the South Fork, where dries, nymphs and streamers all work on the cutthroats and big browns. Casting to the banks with large dries or nymphs works well.

Our favorite fishing is to get out of the boat on numerous gravel bars, islands and side channels to fish to risers in shallow water.

This is the time for good mayfly hatches that cause trout to congregate in the shallows like cars at a football game.

The Madison

July and August are prime time on the Madison, with excellent dry fly fishing to mayflies, caddis and terrestrial like beetles, ants and hoppers.

Both floating and wading will give you chances at browns and rainbows on either dries or nymphs, or fish both with a dry and a dropper. Mornings and evenings can be especially good at this time of year.

It’s definitely not too late to book a stay at the Lodge during August or September.