Souhegan River

The Souhegan River is formed by the convergence of its South and West branches in the town of New Ipswich and flows east for approximately 33 miles before joining the Merrimack River in the town of Merrimack. Along its course, the river passes through Greenville, Wilton, Milford, Amherst, and Merrimack, providing the most accessible quality trout fishing in southern New Hampshire.

The standout feature of the Souhegan is the Delayed Harvest section in Milford, a managed stretch of river running from 300 feet below the Route 31 bridge to 300 feet above the Old Wilton Road bridge. This section operates under special catch-and-release regulations with artificial single barbless hooked lures and flies required during the catch-and-release season. New Hampshire Fish and Game stocks this section heavily with brook, brown, and rainbow trout, creating a concentrated fishery with abundant fish in pocket water, technical glides, and deep pools.

What makes the Milford Delayed Harvest section remarkable is its character. Despite its location in a suburban southern New Hampshire town, this stretch of river resembles a White Mountain stream with fast pocket water, boulder gardens, and short plunge pools. The gradient creates diverse habitat in a compact area, allowing anglers to fish a variety of water types within walking distance of the parking area.

Beyond the Delayed Harvest section, the Souhegan offers productive fishing throughout its length. The upper river near Wilton features small stream character with brook trout and stocked fish. The middle and lower river through Milford and into Merrimack broadens, with longer pools and runs holding brown, rainbow, and brook trout. The entire system is heavily stocked during spring, providing good fishing from opening day through the season.

The Souhegan River is a southern New Hampshire freestone stream with moderate water quality and good habitat structure. Water clarity ranges from 2-3 feet of visibility during normal flows to 4 feet during stable conditions. The river is more turbid than White Mountain streams due to the lower elevation, agricultural land use, and suburban development along portions of its banks.

Water temperatures follow seasonal patterns from near-freezing in winter to the mid-60s F in summer, occasionally reaching the upper 60s during prolonged hot weather. The pocket water sections in the Delayed Harvest area maintain slightly cooler temperatures due to aeration and shade. Cold tributary inputs help moderate temperatures, but the Souhegan is a warmer river than mountain streams to the north.

The substrate is predominantly cobble and gravel with pockets of sand and silt in the slower sections. Insect populations are moderate: caddisflies are the dominant aquatic insects, with mayflies (Blue-winged Olives, Hendricksons, Sulphurs) present but less abundant than in northern rivers. Stoneflies are found in the faster pocket water. The river supports a mixed warm and cold water fish community, with trout coexisting with smallmouth bass, fallfish, and various minnow species in the lower sections.