Thousands of young alewives school in a Maine pond.
Alewives in Maine Thousands of alewives school in a Maine pond. © Mark Berry/TNC

Stories in Maine

The Comeback

Restoring free-flowing rivers in Maine.

Maine’s rivers are experiencing an incredible comeback. In 2009, only 2,331 sea-run fish were counted migrating up the Penobscot River and its tributaries. In the spring of 2017, the count had exploded to 1.9 million fish, thanks to the efforts of The Nature Conservancy, our many partners and supporters.

Maine is one of the last places along the East Coast where sea-run fish migrations can still be restored on a grand scale. We have a remarkable opportunity, unimaginable just a decade ago, to bring those migrations back and restore new life to rivers and communities. We’re off to a great start, but there’s more to do.


Uniquely among east coast states, Maine waters support 12 native species of sea-run fish—species that live in the ocean and travel to fresh water rivers or ponds to lay their eggs, or, like the American eel, spend their lives in fresh water and migrate to the ocean to spawn.

Alewives, Atlantic salmon, American shad, Atlantic sturgeon, Atlantic tomcod, blueback herring, rainbow smelt, sea lamprey, sea-run brook trout, shortnose sturgeon, and striped bass live most of their lives in the ocean, only migrating to fresh water during the spring to spawn. American eels do the opposite—they live in our freshwaters and migrate to the Sargasso Sea to mate, far off the coast of the southern United States. Many of these species may make the trip multiple times during their lives.

These amazing fish bring important ocean nutrients to fresh water ecosystems and provide food for eagles, osprey, kingfishers, otters, seals, and other animals that rely on the river for some or all of their life cycle. Schools of alewives, blueback herring, and shad also provide food for larger marine fish like cod. Many coastal communities enjoy annual alewife and herring harvests for eating and for use as lobster bait. Entire festivals are celebrated each spring in Maine to welcome these fish back to their spawning grounds.


Our rivers were once filled with millions of fish swimming upstream from the ocean every year on their spawning migrations, providing food for people and wildlife. Then, during a long and productive history of industry in Maine, dams were built to harness the river’s power and roads were cut to bring goods and people together. In many places this construction cut off sea-run and other native fish from the types of habitat they need to reproduce and thrive. This among other challenges like water pollution and overfishing have resulted in drastic population declines. Atlantic salmon and shortnose sturgeon are now endangered, Atlantic sturgeon are listed as threatened, and Rainbow smelt, blueback herring, and alewives are considered species of special concern. These blocked waterways don’t only effect migratory fish—dams and poor culverts also impact other wildlife that depend on streams, like native brook trout and turtles.

Open-bottom culvert is lowered into place
Installing an arch culvert An open-bottom culvert is installed over a Maine stream. © Robert Bukaty


Dams and undersized culverts that block water flow can degrade water quality, increase water temperatures, and deplete oxygen. Culverts that are too small and aging dams are vulnerable to storms and flooding that can cause erosion and structural damage. Precipitation has increased across Maine, with more frequent intense storms. Properly designed fish-friendly road crossings reduce flood risk, improve transportation safety, and help minimize short-term repairs cost


The Nature Conservancy in Maine is working with partners to remove barriers to sea-run fish and promote healthy, free-flowing rivers all around the state. This work also enhances and protects riverside communities by offering new economic opportunities, improving state and town road safety, and generally increasing people’s quality of life.

We’re working with partners to:

  • remove or find ways around dams so that the needs of both fish and people are considered.
  • upgrade public and private road-stream crossings to be fish-friendly and storm-resistant.
  • promote policies and regulations that encourage habitat protection and access for fish and wildlife while supporting the communities that depend on clean water and safe roadways.
The Comeback: see how millions of alewives are returning to Maine's rivers.