Acadia's Beavers: Engineers of Mount Desert Island's Wetlands

A beaver in a partly frozen pond. NPS photo by Kent Miller.

A watery island

Mount Desert Island is a watery place, thanks partly to beavers. Park staff and researchers have found more than 250 beaver-influenced wetlands in Acadia National Park. With little room among the steep hills to make new wetlands, beavers expand, connect and diversify existing streams and ponds with their dams — raising water to reach their plant foods and protect their lodges of sticks and mud, and creating habitat for many other plants and animals.

People and beavers

• Travel: when canoes were the main way to get around, beaver-made networks of water let people reach food, medicine and materials.
• 1604: a few Wabanaki people hunting beaver and fishing met the navigator Samuel de Champlain on the shore of the island he would name "Isle de Monts Desert." By his account they traded beaver furs for bread, tobacco and other goods — a sign pelts were still plentiful enough to trade for trifles.
• The fur trade: beaver fur was then among the most valued goods traded between North America and Europe, and demand drove beavers toward disappearance across the continent. Locally they were trapped out by the 1800s, though furs kept coming from inland. In 1882, local papers reported beaver poke bonnets in bronze, green, red, brown, black and white were in fashion, and 10,267 beaver furs had sold in London.

A beaver in its habitat. NPS.

The "Great Drying"

Without beavers, many wetlands dried up and filled with grass, shrubs and trees; water drained faster into stream channels. Geologist Ellen Wohl calls the years from 1600 to 1900, when beavers were trapped out, the "Great Drying." A growing human population also filled in wetlands and built roads across streams and valleys, and most people forgot how to live with beavers — though they lived on in Wabanaki oral history and in place names: Beaver Meadow Pool (below Bubble Pond), Beaver Dam Pool (Bear Brook Pond), Beaver Brook Valley (Otter Creek–Cromwell Brook) and the Beaver Pool behind Sand Beach.

Coming back

• 1921: with the early-1900s wildlife conservation movement, the National Park Service, helped by the Maine Fish and Game Commission, reintroduced beavers to Acadia, starting at Bubble Brook.
• A few years later, Vernon Bailey of the U.S. Biological Survey counted 25–30 across the park — at the Breakneck Ponds, Witch Hole Pond, New Mill Meadows, Eagle Lake and Little Hunters Brook — and found nine occupied or recently used lodges, many dams built on the foundations of dams perhaps one hundred and fifty to two hundred years old.
• As families grew, young beavers spread into the flat valleys, rewatering land and reclaiming meadows from cedar forest. By 1932 they were in Little Harbor Brook and Marshall Brook; in 1934 the Bar Harbor Times reported a large beaver felling trees in the brook above the cemetery bridge.

A birch felled by beavers.

Relearning to share

Infrastructure built in the beaverless years soon clashed with them. Dams flooded paths at Witch Hole Pond, where much of the trail was rerouted, and at Lake Wood, where crews kept clearing dams from a bridge until rising water covered much of the lakeside path. The population recovered so well that the Park Service began trapping beavers, moving some to the mainland. It was the start of people relearning how to live with them.

After the Fire of 1947, abundant new aspen and birch fed a larger beaver population, which peaked around 1980 and settled at about 100.

Managing roads, not beavers

To a beaver, water flowing through a culvert is a leak in its dam system that must be plugged. The Park Service manages infrastructure, not beavers: staff clear clogged culverts and install "Beaver Deceivers" — fencing devices invented in Maine — where streams pass under roads and trails. Otherwise, beavers are left alone.

Why beavers matter

Ecologists now see beavers not as a problem but as key to healthy wetlands:

• tiers of dams slow and spread water, growing the aquatic plants beavers actually prefer to trees;
• complex water flow draws insects, amphibians, fish and birds, and dead trees fill with nest holes;
• sediment settles out, so water downstream runs cleaner and clearer;
• the wetland acts as a sponge, buffering floods and holding water through dry spells.

As writer Ben Goldfarb puts it in Eager, what looks like disorder is really complexity — habitat that benefits nearly every creature. Few visitors see a beaver, but many enjoy the lively, watery landscape they create.

Sources

Based on "Beavers create habitat diversity in Acadia," by Catherine Schmitt, Acadia National Park; published by the National Park Service and in the public domain; rewritten in hubnx's own words. It draws on park survey reports (Bailey 1925, Betros 1963, Johnson 1937), Cunningham and others (2006), Little (2005), the Mount Desert Herald, Ben Goldfarb's Eager (2018) and Leila Philip's Beaverland (2022). Two photographs credited to the author and the Schoodic Institute are not reproduced.