Marlow and Gilsum: the water above Surry Mountain Lake
Most of the trout go in up here. Gabe Gries, a New Hampshire Fish and Game fisheries biologist, wrote in On The Water that the state stocks close to 10,000 rainbows and browns in the Ashuelot each year and that about 4,000 of each species go in upstream of Surry Mountain Lake in Marlow, Gilsum and Surry. His spring spots are the river above and below the Village Pond in Marlow, the stretches along Washington Pond Road and Route 10 in Marlow and Gilsum, and above all the water between Route 10 in Gilsum and Route 12A in Surry, where the river parallels a road locals call River Road but the maps call Gilsum Road or Surry Road depending on the town. The Gilsum Stone Arch Bridge marks the top of it. There are riffles and runs the whole way, a bend pool where Gilsum Road meets 12A, and more water off Dort Road in Surry. The Gilsum gauge on this page sits in this reach. Wild brook trout show up in the main stem in spring, Gries says, but summer temperatures push them back into the tributaries.
Surry Mountain Lake, Keene and Swanzey
Surry Mountain Dam went up in 1941 for flood control, and the 350-acre lake behind it is shallow, five feet on average, with largemouth over six pounds in photographs Gries has seen, pickerel, crappie, big bluegill and a winter fishery. Under the 2026 digest the reservoir has no closed season and allows two trout through the ice. Trout fishing does not resume below the dam until Coombs Bridge in Swanzey, a slow stretch with a few browns that is better from a kayak, and the area below the Colony Mill Dam on West Street in Keene is pickerel and sunfish water. Gries has taken smallmouth and large fallfish in the Westport Rapids in Swanzey. A second gauge, USGS 01158000 just below the dam, reads the regulated release.
Winchester, Ashuelot village and the Hinsdale browns
Below Surry Mountain Lake the state stocks about 900 each of rainbows and browns in Swanzey and Winchester. The fishing picks up at the site of the former dam in the center of Winchester, then in the riffles on either side of the Ashuelot Covered Bridge on Route 119 in Ashuelot village, and between and below the two upper dams on Route 119, dark water with big slippery boulders, deep pools, and enough insects, minnows and crayfish to hold trout over. Three dams between Swanzey and Hinsdale have come out in the last fifteen years for shad and eel passage. The lower river below the Fiske Mill Dam in Hinsdale was never stocked until a local angler, Roger Blair, proposed it in 2002; after a summer of temperature data the state tried it in 2003, his angler diary showed holdovers the next year, and Gries now calls this reach the best chance on the river for a large holdover brown, alongside walleye and smallmouth that get bigger toward the Connecticut. The mouth is a spring walleye and bass spot and a summer channel catfish spot.
The South Branch fly-only water
The one section of the system with its own gear rule is on the South Branch, not the main stem: from the Marlborough Road bridge in Troy to the Old Richmond Road bridge in East Swanzey it is fly fishing only, two trout, 12-inch minimum. Gries says the South Branch gets 2,500 browns a year in Troy and Swanzey and that this stretch holds fish well into the fall, which makes it the place to go when the main river has warmed.
Forty to 200 cfs at Gilsum
This is a small river above the lake and it runs off fast. The USGS record at Gilsum has typical monthly flows of about 370 cfs in April, 155 in May, 60 in June, 20 to 26 from July through September, 42 in October and 100 to 125 in the late fall and winter. No shop publishes a wading range, so this page compares the live Gilsum reading to 40 to 200 cfs, the band between the May stocking-season flow and the early-summer base, and says so plainly: the April number is snowmelt and hard to fish, the August number is a trickle in which the trout are in the deepest pools or gone to the brooks. The lower river at Hinsdale, USGS 01161000, runs several times higher and is the gauge to watch for the browns and walleye there.
General rules, and the hatches nobody has charted
Apart from the reservoir and the South Branch section the Ashuelot is under New Hampshire's general river rules: trout season January 1 to October 15, five fish or five pounds and no length limit, the river closed to all fishing from October 16 through December 31, no fishing from the ice, and bass catch and release from May 15 to June 15. Walleye carry a two-fish limit and an 18-inch minimum. On hatches the honest answer is that no shop or chart covers the Ashuelot by name. The rows below follow FlyFishFinder's statewide New Hampshire calendar for lower-elevation southern rivers, Hendricksons in early May, caddis through the season, Sulphurs and Cahills in June, terrestrials from July and olives in April and October, and they are marked unverifiable until someone local publishes better.