This spring, for the first time in more than two centuries, American shad, striped bass, and river herring may spawn in White Clay Creek, a tributary of the Delaware River in northern Delaware. Early one morning last month, a five-person crew waded into the frigid creek and pulled down most of a timber-and-stone dam that had blocked the river's flow since the early years of the Revolutionary War.

The White Clay Creek dam was the first ever removed in the state of Delaware, but it was far from the only one removed in the United States last year. On Tuesday, the conservation group American Rivers announced that 72 dams were torn down or blown up in 2014, restoring some 730 miles of waterways from California to Pennsylvania.

Twenty years ago, dam removal was a fringe notion, and early demolition efforts gained support only because the dams in question were no longer in use and, in some cases, were dangerous to people living nearby.

Now, the U.S. dam removal movement has wide acceptance as well as bigger ambitions; on Tuesday, producers of a recent documentary called DamNation met with members of Congress and White House officials to press their case for the removal of four large federal dams from the lower Snake River in eastern Washington.

Small Challenges

While public attention focuses on the most spectacular dam demolitions, such as the removal of the last section of the 210-foot-high Glines Canyon Dam on the Elwha River in Washington state last summer, most of the 865 dams removed in the United States during the past 20 years are small structures originally built for flood control, irrigation, or very local hydropower. The White Clay Creek dam, built to run a long-gone flour mill, was only eight feet tall at its highest point.

But small dams can stop fish as effectively as big ones. Gerald Kauffman, of the Water Resources Agency at the University of Delaware, remembers watching hickory shad bumping their snouts against the downstream face of the White Clay Creek dam, trying and failing to swim upstream to spawn.

Small or large, every dam-removal project has its particular challenges. Some dams, like the one on White Clay Creek, are historic structures that must be carefully surveyed and partially preserved; others have trapped vast amounts of sediment and debris, and must be removed gradually so as not to harm fish, wildlife, and people downstream.

Removals also require support from the dam owners and from nearby communities, state and federal permits, and, finally, money for demolition. The dismantling of the White Clay Creek dam, a relatively small project, cost $210,000. Serena McClain of American Rivers, which helped fund the White Clay removal, says it typically takes three years to plan and execute a removal.

Large dam removals, like those just completed on the Elwha River and proposed for the lower Snake River, take much longer: For well over a decade, scientists and environmentalists have criticized the federal Snake River dams for their devastating effects on salmon.

Spectacular Time Lapse Dam "Removal" Video The White Salmon River in Washington state began flowing again in 2011, after the nearly 100-year-old Condit Dam was disabled by an explosion—a 2-hour process condensed into this 2-minute time-lapse video. (Andy Maser Films)

Dam Defenders

But the Snake River dams and their reservoirs have influential defenders, since they provide transportation and irrigation water to inland wheat farmers and contribute hydropower to the region's electricity supply. Removal is gaining support, but it remains a long way away.

While few removals are as complex or challenging as those proposed for the lower Snake, dam-removal advocates are tackling more controversial projects than they used to.

"We're trying to work more strategically, to have the biggest impact with limited funds and limited people," says McClain. "So we're looking not just at old and outdated dams, but at dams that currently serve a purpose." Many dams now targeted for removal still supply some services to humans, and those services must be replaced in order to win public backing for approval.

The dam-removal movement is also beginning to shift its strategy toward watershed-wide restoration efforts involving multiple dams. To date, five dams have been removed from the Des Plaines River in Illinois, and six more are scheduled to come down.

The White Clay Creek dam demolition is the first of several anticipated removals on the creek. Some states, notably Pennsylvania, have encouraged these broader restoration projects by streamlining their permitting processes.

Support for river restoration through dam demolition is also growing in Europe and Japan. But some countries in Latin America, Africa, and Asia continue to propose and build large hydropower dams, both to meet domestic power demand and to produce electricity for export.

And some 80,000 dams taller than six feet-along with tens of thousands of smaller dams-still obstruct U.S. rivers. Former Interior Secretary Bruce Babbitt, a proponent of dam demolition, once observed that "on average, we have constructed one dam every day since the signing of the Declaration of Independence."

One of the first of those was the White Clay Creek dam, built in 1776 or 1777 by the mill owner and Quaker minister Daniel Byrnes. Byrnes's nearby house was the site of a historic meeting on September 6, 1777, when George Washington, the Marquis de Lafayette, and several other Continental Army officers gathered there to plan the defense of Philadelphia. Though Washington lost the subsequent battle against the British, he won the war. Today, the same might be said of White Clay Creek.