A tiny fish once at the center of a controversy over the Endangered Species Act has officially recovered — a rare victory for the conservation movement at a time when so many species are disappearing across the planet.

The U.S. Fish and Wildlife Service recently announced the snail darter has a robust enough population to remove it from the nation’s list of imperiled wildlife. Originally declared endangered in 1975 due to the threat posed by the construction of the Tellico Dam in Tennessee, federal wildlife officials now argue the fish is no longer at risk of extinction after being transplanted to other rivers and discovered in locations beyond the dam’s reach.

The minuscule freshwater fish was the subject of a major legal battle that ended with the Supreme Court ruling the federal government had to protect imperiled plants and animals “whatever the cost.” The 1978 decision against a dam developer showed the American public — including real estate developers, oil drillers and other business leaders whose work affects imperiled plants and animals — the power of the Endangered Species Act.

“I’ve been doing this for 28 years now and this is stuff that we studied in college — the whole controversy,” said Kristi Young, a deputy manager for the Service’s Division of Conservation and Classification. “The first Supreme Court case showed that the Endangered Species Act meant business.”

The successful recovery of the fish found in the Tennessee River and its tributaries is the culmination of a decades-long recovery effort. Wildlife advocates are now pointing to the once-reviled snail darter to counter criticism from Republican lawmakers and business groups who consider the Endangered Species Act costly and ineffective.

But the recovery of this single fish species comes as U.N. scientists warn that around 1 million other types of animals and plants worldwide are threatened with extinction — many within decades — as their habitats are destroyed and temperatures rise due to human-caused climate change.

“Really, most species don’t have time to recover,” said Tierra Curry, senior scientist at the Center for Biological Diversity, a green group that petitioned the Fish and Wildlife Service in 2019 to declare the snail darter saved. “This species was one of the first listed. It took 45 years.”

The landmark 1973 law made it illegal to harm endangered species or eliminate their habitats. The construction of the Tellico Dam on the Little Tennessee River — which halted the free flow of water needed by the snail darter and displaced hundreds of nearby farmers from their land — proved to be an early test for the law’s reach.

Despite environmentalists’ victory in the case, though, the dam was finished. After the ruling, Congress stepped in to exempt the project, built by the Tennessee Valley Authority, from complying with environmental laws.

Yet since the dam’s completion, the federally controlled TVA has worked to raise oxygen levels in more than 300 miles of river downstream of its dams — a move meant to improve the viability of the 3-inch fish — while wildlife managers successfully introduced the snail darter in the Hiawassee and Holston rivers. The brown, bottom-dwelling fish, with a telltale teardrop-shaped mark below its eye, is named after the mollusks it preys upon.

During its half-century on the books, the Endangered Species Act is credited with saving the bald eagle, American alligator, humpback whale and now the snail darter. Yet Republicans have long lambasted the law, since only a fraction of the more than 1,600 species declared imperiled ever made it off the list.

Jonathan Wood, vice president of law and policy at the Property and Environment Research Center, a free-market environmental think tank, said it is “easy to overstate” the role the Endangered Species Act played in saving the snail darter since wildlife managers originally underestimated the fish’s range. “The Service was just wrong about how many darters are out there.”

Heeding the call of loggers, ranchers and other business interests, officials under President Donald Trump watered down several long-standing protections under the law. The Trump administration, for instance, wanted to allow wildlife managers to take the economic cost of conservation into account when deciding whether to protect a species. In June, President Joe Biden’s team announced plans to reverse those policies.

Zygmunt Plater, a lawyer who originally petitioned the government in the 1970s to declared the snail darter endangered, said the Fish and Wildlife Service’s announcement shows the law “is not the joke that many politicians have tried to make it.” But he added most species should be saved by preserving their existing habitat — not by relocating them.

“Scientifically, transplantation is not a sure thing,” said Plater, now a professor at Boston College Law School. “Conservation of natural habitat is in virtually all cases a better solution.”