Inside the park, rainbows go back
In Yosemite National Park and the El Portal Administrative Site, the National Park Service sets its own rules for the Merced, the South Fork Merced and their tributaries. Only artificial lures or flies with barbless hooks may be used. Rainbow trout, native at Yosemite's lower elevations, are catch-and-release only and should not be lifted from the water. Brown and brook trout may be kept, 5 a day and 10 in possession, and new for 2026, keeping them is optional rather than expected. Any bait is banned, including scented lures and manufactured eggs, lead weights must be a quarter ounce or less, and you may not fish from any bridge.
The Park Service page now says all park waters are open all year unless noted. Some guide and shop pages still describe a stream season from the last Saturday in April to November 15; the park's page is the one that counts, and a California license is required for anyone 16 or older.
Valley pools, then eight miles of gorge
Sierra Fly Fisher's guide to Yosemite puts the catch in the valley at about three rainbows for every brown. Most of its author's time has been spent just downstream of Yosemite Valley, where long, slow pools give way to pocket water and deep runs for about a mile before the river drops into the Merced Gorge. The gorge runs roughly eight miles beside Highway 140 with very few turnouts, steep rocky walls, boulders and log jams, and hard scrambling to reach the water. The payoff is solitude: the writer rarely saw another fly angler there.
The guide's timing is to wet-wade the gorge from late June or early July, once runoff drops. The year starts earlier than most people expect: small Blue-Winged Olives on warm days in late January and February, and the first Golden Stoneflies in February. The South Fork at Wawona, along Highway 41 and up the road to the Swinging Bridge area, holds plenty of rainbows and browns that average about six inches, with brook trout higher up, and suits a beginner in late spring.
Out of the park: the statewide stream rules
Once you leave the El Portal Administrative Site, the Park Service rules stop and California's apply. The 2026 freshwater booklet lists no special regulation for the Merced between the park and Lake McClure, so the statewide stream rule covers the canyon: open from the last Saturday in April through November 15 with 5 trout a day and 10 in possession and no gear restrictions, then from November 16 to the Friday before the last Saturday in April a zero bag limit, with only artificial lures on barbless hooks for all species. Released fish should stay in the water.
Snelling, Crocker-Huffman Dam and the salmon hatchery
Below Lake McClure the Merced becomes a valley river, and the booklet splits it at the Schaffer Bridge on Oakdale Road. From Crocker-Huffman Dam down to the Schaffer Bridge it is open January 1 through October 31, artificial lures with barbless hooks only, 2 hatchery trout or hatchery steelhead a day and 4 in possession. Hatchery fish are the ones with a healed adipose fin clip; every other trout or steelhead goes back. From the Schaffer Bridge to the mouth the season and limit are the same, bait is allowed, and from April 1 through the Friday before the fourth Saturday in May bait hooks are restricted by gap size. Both reaches close November 1 through December 31.
CDFW's Merced River Hatchery near Snelling is a Chinook salmon facility, and its ladder usually opens to spawning fish around October 1. To visit, take Highway 59 north from Merced, turn right on Snelling Road and left on Robinson Road, then follow the canal-bank road about three miles.
Pohono Bridge in September
USGS 11266500 sits at Pohono Bridge at the downstream end of Yosemite Valley, which makes it the gauge for the valley and the head of the gorge. Snowmelt dominates it: monthly means since 2010 are about 1,540 cfs in April, 2,240 in May, 1,800 in June and 630 in July, then 140 in August, 53 in September and 100 in October. No shop publishes a wading range, so the 50 to 650 cfs band here is the July through October span of those means, the wet-wading months the guide recommends. On September 24, 2026 Pohono read 16.5 cfs, far below the September mean, and the Happy Isles gauge upstream read under 6. Sierra Fly Fisher notes that South Fork trout spook more easily when the water gets very low in the fall; at 16 cfs, go small and keep your distance.