Broad forest-lined river in northern Maine at sunrise

Ecology · Rivers

Penobscot River

A river system shaped by two great branches, forested headwaters, working communities, dams, fisheries, and a long journey toward Penobscot Bay.

River overview

A watershed across northeastern Maine

The Penobscot River basin drains approximately 8,680 square miles. Its main stem runs about 105 miles from the meeting of the East and West Branches in Medway south to Penobscot Bay.

Much of the watershed is forested and sparsely populated. Its rivers and tributaries connect northern lakes and woods with communities including Millinocket, Howland, Lincoln, Old Town, Orono, Veazie, Bangor, and Brewer.

Main stemAbout 105 milesFrom Medway to Penobscot Bay

WatershedAbout 8,680 sq. mi.A large northeastern Maine drainage basin

Two headwater routesEast & West BranchesMeeting at Medway

LandscapePredominantly forestedLakes, tributaries, towns, and tidal reaches

Drainage by river

The following figures describe the drainage areas traditionally reported for the principal portions of the river system.

East Branch Penobscot River1,150 sq. mi.

West Branch Penobscot River2,140 sq. mi.

Mattawamkeag River1,520 sq. mi.

Piscataquis River1,470 sq. mi.

Penobscot River2,400 sq. mi.

Ecology and change

The river historically supported abundant alewives, shad, and Atlantic salmon. Dams, pollution, and overfishing reduced migratory fish populations and altered connections between the river, its tributaries, and the Gulf of Maine.

The watershed remains a linked system: conditions upstream influence habitat and water quality downstream, while the river’s lower reaches connect inland Maine to Penobscot Bay.

Windows on the river

From headwaters to the bay

These views interpret the river’s changing character: secluded northern water, fast-moving forest reaches, broad community crossings, and the lower river near the coast.

Quiet northern lake surrounded by forested hills — Forest and lake country characterize the Penobscot headwaters.

Mountain river flowing through dense evergreen forest — Tributaries and branch channels carry water through Maine’s northern woods.

Wide river winding between wooded banks — The main stem widens as it moves south from Medway.

River valley beneath a broad blue sky — The watershed links remote landscapes with settled river communities.

Sunlight filtering through dense northern forest — Forests cover much of the basin and shape its streams and shorelines.

Coastal water opening toward the sea — The lower Penobscot opens toward Penobscot Bay and the Gulf of Maine.

The two branches

Separate routes to Medway

The East and West Branches traverse distinct headwater landscapes before joining to create the Penobscot’s main stem.

Northern forest descending to a river valley

East Branch

The East Branch originates above Grand Lake Matagamon and passes east of Baxter State Park. Its route includes T6 R8 WELS, the T3 R7 WELS area, Soldiertown Township, and Grindstone Township before reaching Medway.

Mountain lake and river corridor surrounded by forest

West Branch

The West Branch begins in the Seboomook Lake region, where the North and South Branches meet. It passes through Seboomook Township, Northeast Carry Township, T2 R10 WELS, T3 R11 WELS, and T4 Indian Purchase Township. It continues by Millinocket and East Millinocket before joining the East Branch.

Follow the water

Four stages of the river system

A simple route from remote headwaters through branch corridors and the main stem to tidewater.

Headwater lakes

Northern lakes and ponds collect water from forested uplands.

Two branches

The East and West Branches follow separate routes through the interior.

Medway confluence

The branches meet at Medway and form the river’s main stem.

Penobscot Bay

The river passes communities and tidal reaches before opening to the bay.

Reference notes

Sources behind the overview

The original entry drew on state and federal river-basin and biomonitoring materials.

Maine Department of Agriculture, Conservation and Forestry

Maine River Basin Report, “Penobscot River Basin,” 2007.

Maine Department of Environmental Protection

“Biomonitoring Retrospective of the Penobscot River,” 1999.

National Oceanic and Atmospheric Administration

Regional watershed material concerning the Penobscot River system.

FAQ

Understanding the Penobscot

Quick answers about the watershed, branches, route, and environmental context.

Where does the Penobscot River begin?

The main stem begins at Medway, where the East and West Branches meet. Each branch has its own northern headwater system.

Where does the river end?

The river flows south through central and coastal Maine and enters Penobscot Bay.

How large is the watershed?

The basin drains approximately 8,680 square miles in northeastern Maine.

What communities lie along the basin?

Major communities include Millinocket, Howland, Lincoln, Old Town, Orono, Veazie, Bangor, and Brewer, along with numerous smaller communities and townships.

Why are the East and West Branches important?

They drain different northern landscapes and meet at Medway to form the main stem. Together they account for a substantial part of the full watershed.

What fish are associated with the river?

The river historically supported migratory fish including alewives, shad, and Atlantic salmon. Dams, pollution, and overfishing altered their abundance and access to habitat.