Cobscook Bay is located in Washington County in the state of Maine. It opens into the Bay of Fundy immediately south of the city of Eastport and adjacent to Passamaquoddy Bay. In the 1930s, Cobscook Bay was part of the aborted Quoddy Project to generate electricity from its large tidal range.
Cobscook Bay is a large area of estuary in Washington County, Maine that opens into the Bay of Fundy through a relatively narrow opening. It is about 10 miles (16 km) long and 10 wide and has a long, convoluted coastline with many islands. The largest municipality is Eastport, which is on Moose Island at the mouth of the bay and is joined to the mainland by a causeway. It is the easternmost city in the United States and is connected to the neighbouring province of New Brunswick, Canada by a ferry service. Other townships around the bay are Perry, Pembroke, Dennysville, Edmunds, Tresscott and Lubec. There are about 7,000 people living in the nine communities in the area, many of whom are fishermen or work in fish farming, shipping or tourism. There is a scallop fishery here.
The bay is both geologically and hydrologically complex. The tide has an average range of 24 feet (7.3 m) and there are strong currents as large volumes of sea water flow into and out of the bay twice a day. The bay is very shallow with the average depth being about 10 metres (33 ft) and about one third of its area is exposed at low water. The volume of freshwater entering from streams is relatively small and the nutrient rich waters support a great diversity of phytoplankton and algae. These support a biodiverse community of fish, shellfish, marine worms and other invertebrates. Many birds feed on these and the bay is an important visiting place for migrating birds and waterfowl.
The area surrounding the bay is well-timbered, but as well as forests there are streams, lakes, bogs, marshes and mudflats interspersed by a network of trails.
Communities around the bay were traditionally involved in shipbuilding, logging, farming, fishing and trading.
In 1935, there was a proposal to build a barrage to harness the power of the tides in the area. Dams were envisaged to impound the waters of Cobscook Bay and the adjoining Passamaquoddy Bay. Construction was started and some dikes were built, but a year later, the United States Congress withdrew its support and funding and the scheme was abandoned. The Quoddy Dam Model Museum at Eastport houses exhibits with information on the project.
The generation of electricity from the bay's tidal currents was ultimately accomplished in September 2012. A turbine has been installed in Cobscook Bay near Lubec that is capable of generating 180 kW of electricity, and is the first North American commercial tidal energy project to supply power to the electrical grid. The turbines do not need dams to be built in order to function and are mounted on the sea bed. The turbine blades spin slowly in the current and testing seems to indicate they are harmless to marine life. Two more turbines are planned for installation in the bay within a year's time.
This coastal area is home to many resident birds. One of these is the bald eagle (Haliaeetus leucocephalus) and Cobscook Bay has more pairs of these rare birds per square mile than the rest of Maine. It also houses 25% of the state's black duck (Anas rubripes) population. In the fall, the bay is used by large numbers of birds migrating southwards from their summer breeding grounds. Rare species of bird to be seen here include the harlequin duck (Histrionicus histrionicus). An invertebrate of special concern is the mystery snail (Vertigo paradoxa), an air-breathing land snail. In the summer several species of whale enter the bay, including the minke, fin whale and right whale.
Efforts are being made to preserve the biodiversity of the bay. A 250-foot (76 m) buffer zone has been created adjacent to the foreshore where no development is allowed. The alewife (Alosa pseudoharengus) is a species of anadromous fish which goes upstream to spawn. Efforts are being made to enable these fish to reach their traditional spawning grounds in the upper waters of the Pennamaquan River, Little River and Boyden Stream. These fish are thought to be important in the bay's ecosystem by providing food for the eagles.
 Other uses of the name
"Cobscook Bay" is also the title of a song by The Mountain Goats from their EP Isopanisad Radio Hour.
- "Cobscook Bay". Maine Government. Retrieved 2012-12-25.
- "Cobscook Bay Resource Center". Retrieved 2012-12-27.
- "Down East: The nature of Maine". Cobscock Bay Area Chamber of Commerce. Retrieved 2012-12-27.
- "Quoddy Dam Model Museum". Border Historical Society. Retrieved December 27, 2012.
- Woodard, Colin (September 13, 2012). "Maine tidal turbine goes online, first in North America". Portland Press Herald. Retrieved January 1, 2013.
- Woodard, Colin (July 22, 2012). "Maine company leading way as tidal energy comes of age". Portland Press Herald. Retrieved December 27, 2012.