Question: What river does West Swanzey Covered Bridge cross and is a tributar of the Connecticut River?

Context paragraphs:
Bedell Covered Bridge: The Bedell Bridge was a Burr truss covered bridge that spanned the Connecticut River between Newbury, Vermont and Haverhill, New Hampshire.  Until its most recent destruction in 1979, it was, with a total length of 382 ft , the second-longest covered bridge in the United States.  The bridge was divided into two spans of roughly equal length, and rested on a central pier and shore abutments constructed from mortared rough stone.  The eastern abutment has been shored up by the addition of a concrete footing.  The bridge was 23 ft wide, with a roadway width of 18.5 ft .  Because the state line is the western low-water mark of the Connecticut River, most of the bridge is in New Hampshire; only the western abutment is in Vermont.

Kurtz's Mill Covered Bridge: The Kurtz's Mill Covered Bridge is a covered bridge that spans Mill Creek in the Lancaster County Park in Lancaster County, Pennsylvania, United States.  The bridge is also known as the County Park Covered Bridge, Baer's Mill Covered Bridge, Isaac Baer’s Mill Bridge, Keystone Mill Covered Bridge, Binder Tongue Carrier Covered Bridge, and Mill 2A Covered Bridge.  The bridge is accessible to road traffic from within the park.

West Swanzey Covered Bridge: The West Swanzey Covered Bridge (also known as the Thompson Bridge) is a historic wooden covered bridge carrying Main Street over the Ashuelot River in West Swanzey, New Hampshire.  The two-span Town lattice truss bridge was built in 1832 by Zadoc Taft for the town at a cost of $523.27.  It is 136'10" long, with spans measuring 64'0" and 63'6", and rests on a stone central pier and abutments.  Unusual for surviving covered bridges, the bridge occupies a central location in the village of West Swanzey, and was originally equipped with two sidewalks (it now has only one).  In 1973 the bridge was posted for a six-ton limit, requiring school buses to empty before they could cross the bridge.  It was closed to all traffic in 1990, but has since been rehabilitated and reopened.

Cornish–Windsor Covered Bridge: The Cornish–Windsor Covered Bridge is a covered bridge that spans the Connecticut River between Cornish, New Hampshire and Windsor, Vermont.  It was the longest covered bridge still standing in the United States until the Smolen–Gulf Bridge opened in Ohio in 2008.

Enfield–Suffield Covered Bridge: The Enfield–Suffield Covered Bridge was a wooden covered bridge over the Connecticut River located between Enfield, Connecticut and Suffield, Connecticut.  This bridge connected Bridge Lane on the Enfield (east) side of the river with the west side of the river, where Bridge Street met it.  There is now a parallel row of trees on this west side of the river where the street once ran.

Kintersburg Covered Bridge: The Kintersburg Covered Bridge is a covered bridge spanning Crooked Creek in Rayne Township, Indiana County, Pennsylvania, United States.  Built in 1877, it is one of four covered bridges in the county, and is the only one with a Howe truss design.  It is 62 ft .  The Howe design is rather rare in covered bridges.  The Kintersburg Bridge is one of only five in the state of Pennsylvania with that design.  The other four are the McConnell's Mill Covered Bridge in Lawrence County, Mean's Ford Covered Bridge in Bucks County, St. Mary's Covered Bridge in Huntingdon County, and the Thomas Mill Covered Bridge in Philadelphia County.

Columbia Bridge (New Hampshire): The Columbia Bridge is a covered bridge, carrying Columbia Bridge Road over the Connecticut River between Columbia, New Hampshire and Lemington, Vermont.  Built in 1911-12, it is one of only two New Hampshire bridges (along with the Mount Orne Covered Bridge) built with Howe trusses, and is one of the last covered bridges built in the historic era of covered bridge construction in both states.  It was listed on the National Register of Historic Places in 1976.

Swanzey, New Hampshire: Swanzey is a town in Cheshire County, New Hampshire, United States.  The population was 7,230 at the 2010 census.  In addition to the town center, Swanzey includes the villages of East Swanzey, West Swanzey, North Swanzey, and Westport.

Pittsburg–Clarksville Covered Bridge: The Pittsburg–Clarksville Covered Bridge (also known as the Bacon Road Bridge) is a wooden Paddleford truss bridge with added arches over the Connecticut River located between Pittsburg and Clarksville, New Hampshire.  It was closed to traffic in 1981.  The bridge is the northernmost covered bridge crossing the Connecticut River.

Ashuelot River: The Ashuelot River is a tributary of the Connecticut River, approximately 64 mi long, in southwestern New Hampshire in the United States.  It drains a mountainous area of 425 sqmi , including much of the area known as the Monadnock Region.  It is the longest tributary of the Connecticut River within New Hampshire.

Supporting paragraphs: West Swanzey Covered Bridge Ashuelot River
Answer: Ashuelot River