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Cobscook Bay: An Extraordinary Estuary with “Boiling Tides”

By Michael Johnson, Northeast Regional Office Habitat Conservation Division

An urchin dragger working in Half-Moon Cover near the site of a proposed tidal power barrage near Eastport, ME.  Photo Credit: NOAA

Diverse Ecosystem

Cobscook Bay is a shallow estuary comprised of about 200 miles of rugged, rocky, and convoluted shoreline located in the easternmost portion of Maine.  Adjacent to the Canadian border, this area is known as “Downeast Maine.”  About 7,000 people live in the nine communities surrounding Cobscook Bay, and most are fishermen, or work in fish farming, tourism, and shipping.  The Cobscook Bay area is primarily rural, and supports a relatively intact and ecologically-diverse community of fish, shellfish, migrating birds and waterfowl, and invertebrates such as marine worms, crabs, and lobsters. 

The area is home to important fish species such as Atlantic herring, winter flounder, Atlantic cod, and haddock, as well as anadromous fish including alewife, blueback herring, and rainbow smelt.  These anadromous fish live within the Cobscook Bay estuary until they reach maturity, and then make annual spawning migrations into the freshwater rivers and streams that flow into the bay.  They serve as food for larger species, including Atlantic cod, haddock, bluefin tuna, bluefish, sea birds, and marine mammals like seals.  Cobscook Bay is also a vital center for Maine's aquaculture industry because it provides prime habitat for sea scallops, sea urchins, and soft-shelled clams.

  Massive Tides

Cobscook Bay is equally well known for its impressive tides.  In fact, Cobscook is the Maliseet-Passamaquoddy tribal word for “boiling tides.”  The tidal range in the bay averages 24 feet and can exceed 28 feet (the average tide range is about 1.8 feet in Waquoit Bay, Massachusetts).  Although Cobscook Bay tides are not as extreme as those of nearby Bay of Fundy, where the tides can exceed 50 feet, strong currents here bring in and flush out a large volume of sea water twice daily.  These massive tides and strong currents have shaped the coastal landscape and ecology of the Cobscook Bay.   Efforts to harness this water power to generate electricity began with a proposal to build barrage dams across both Cobscook Bay and Passamaquoddy Bay in 1935.  (Barrages are used to dam a lagoon or estuary as a method to capture tidal power from tidal inflows.)  Although construction was initiated, the U.S. Congress withdrew its support and funding and the project was abandoned.  Other efforts to develop tidal energy have since been attempted, but none have been successful due to the extraordinary costs and the harmful ecological effects of damming the estuary.

Proposed location of a tidal power barrage in the Pennamaguan River estuary, near Pembroke, ME.  Photo credit: NOAA.

Harnessing Tidal Power

Growing energy prices in recent years have renewed interest in developing tidal energy in Cobscook Bay.  Currently there are two proposed barrage dam projects in Half-Moon Cove near Eastport, Maine, and in the Pennamaquan River estuary near Pembroke, Maine.  Both of these projects are undergoing review through the Federal Energy Regulatory Commission’s (FERC) licensing process.  Although a final licensing decision by FERC is several years away, NOAA Fisheries staff has recommended numerous studies be undertaken by the project proponents to help evaluate the potential effects of these projects on fisheries and habitats within the Bay. 

Rance Tidal Power Station is the world's first.  Located on the estuary of the Rance River in Brittany, France.

With the installation of an underwater turbine in Cobscook Bay near Lubec, Maine, the first North American commercial tidal energy project was implemented and is now supplying power to the electrical grid.  The novel design of this underwater turbine allows tidal power generation without the need to construct a dam.  The turbines are mounted on the sea floor and spin slowly in the current.  Initial testing and monitoring indicate they may not harm fish or marine mammals.  Additional turbines are planned for deployment in nearby Western Passage.  Additional monitoring will be required to evaluate the effects of the devices on estuarine and marine species, including threatened and endangered species that inhabit the Bay. 

NOAA Fisheries continues to assess this new technology as the testing is expanded.  If it can be developed without adversely affecting estuarine and marine ecosystems and organisms, tidal power generation offers an abundant source of clean, renewable energy.