Wompatuck State Park – Aaron River Reservoir and Dam

Wompatuck Entrance (The Res), 558 Beechwood St, Cohasset, MA 02025, USA

(617) 895-8245

Owned By: Commonwealth of Massachusetts

This entrance to Wompatuck State Park offers direct access to the Aaron River Reservoir. Hike up the steep hill beside the spillway for an incredible view. You can walk across the top of the 900-foot wide, 25-foot tall dam, and down the other side (about 0.4 miles round-trip). An additional trail to the side leads to the Doane Street entrance to Wompatuck.

The reservoir is open for fishing and non-motorized boating. The top of the dam is stroller-friendly, but ascending the hill could be a challenge!

The park’s other access points include: Main Entrance, Hingham • Leavitt Street Entrance, Hingham • Triphammer Pond Conservation Area, Hingham • Whitney Spur Rail Trail, Cohasset • Whitney & Thayer Woods, Cohasset • Doane Street Entrance, Cohasset • Brass Kettle Conservation Area, Cohasset •  Grove Street, Norwell • Mt. Blue Street, Norwell


The Aaron River Reservoir is a back-up water supply for the Town of Cohasset. While designated as a Class A water supply source, it is contaminated with mercury from an unknown source.

The 3,500-acre Wompatuck State Park served as the Hingham Naval Ammunition Annex from 1941 to 1965. It stretches into four towns – Hingham, Cohasset, Scituate and Norwell. The park features numerous seasonal campsites. There are 12 miles of paved bike paths, plus off-road trails for hiking, mountain biking, horseback riding and cross-country skiing. This entrance offers one trail that connects with the larger park.

The land at Wompatuck State Park was commonly used by the Massachusett tribe, led by Chief Josiah Wompatuck. English settlers purchased the land from Wompatuck in 1655. In the 1700s, early settlers and ship captains held title to the area, but the land was never extensively developed. During the 1800s, families maintained woodlots and grazing lands here, and the streams powered the Stockbridge Shingle Mill. Water from Mt. Blue Spring was commercially bottled.

In 1941, the United States government established the Hingham Naval Ammunition Depot Annex (known by locals as the “Cohasset Annex”) on the site. Land was acquired from private homeowners for the purpose of expanding the Hingham Naval Ammunition Depot nearby (see for details, see listing for Bare Cove Park). It remained in use until 1965, and served both World War II and the Korean Conflict.

Scattered throughout the property are over 100 decommissioned military bunkers, which were used to store ammunition. Explosives such as TNT-loaded depth charges, bombs, fuses, projectiles, and cartridges were produced and stored here. Many of these bunkers have been backfilled, but some remain exposed. There are several old military buildings on the property, as well as an abandoned railroad. Most buildings have had their roofs and windows removed and are open to the elements.

The U.S. Navy deactivated the Cohasset Annex in 1963 and declared the land as surplus. The Commonwealth of Massachusetts took possession of the land in 1966, and began developing it as a public park the following year. The park itself opened in 1969. Since then, 725 acres have been added.

The Mount Blue Spring is currently closed. Typically, the Mt. Blue Spring is open seasonally, featuring water drawn directly from a natural aquifer. You can find it in a shed with an adjacent parking area, on Union Street in the park, between markers E14 and E1, not far from the Transfer Station area. The water is tested frequently for safety.

Trail Description

This entrance offers a steep uphill trail to the top of the dam, and a wide unpaved road extending across the top of the 900-foot dam (about 0.32  mile altogether, or a 0.45 mile circuit if you work your way down the other side, across the grass). At the foot of the dam, there is an additional path that crosses the Aaron River and connects with additional trails at the Doane Street (Cohasset) entrance to the park, as well as the park’s more extensive trail network. Plus there is additional pedestrian access from Aaron River Road.

Wompatuck offers numerous woodland trails for hiking, dog-walking, horseback riding, cycling, and cross-country skiing. For mountain bikers, the park is home to one of the longest section of switchbacked singletrack in the state. The Wompatuck Trail is ADA accessible.

Habitats and Wildlife

The Aaron River finds its source within Wompatuck State Park and flows northeast to the Aaron River Reservoir. The dam that holds the reservoir in place was constructed from 1976-1978. Below the dam, the river continues to flow through Cohasset. It joins with Brass Kettle Brook and eventually empties into the Gulf River in North Scituate. The Gulf River flows into the ocean at Cohasset Harbor.

Wompatuck Entrance (The Res), 558 Beechwood St, Cohasset, MA 02025, USA

Historic Site: No

Park: Yes

Beach: No

Boat Launch: Yes

Lifeguards: No

Size: About 0.4 miles of trail, with direct link to additional trails throughout the 3500-acre state park.

Hours: Dawn to dusk.

Parking: Limited on-site parking at the end of Beechwood Street.

Cost: Free

Trail Difficulty: Medium


Informational kiosk. Trash barrels. Two benches at the top of the dam. Geocache locations. The Mount Blue Spring is currently closed.

Dogs: Dogs must be leashed at all times. Scoop the poop!

Boat Ramp: No

ADA Access: No

Scenic Views: Yes

Waterbody/Watershed: Aaron River (Gulf River/Cohasset Harbor watershed)

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