A FTER WITNESSING near-biblical calamities, Congress passed the Clean Water Act in 1972. The Cuyahoga river in Ohio caught fire in 1969. That same year 26m fish died in Florida’s Lake Thonotosassa, the largest recorded fish kill, because of pollution from food-processing plants. “Dirty Water”, a song from that era about the repellent Charles river, remains an anthem of Boston sports teams to this day. Since the early 1970s the White House has interpreted the statute in different ways. President Donald Trump’s team, who released a draft rule on December 11th, apparently want to take water law back to the 1980s.

Despite the simple intentions of the Clean Water Act, its language was anything but. It sought to eliminate the discharge of toxic pollutants into “waters of the United States” ( WOTUS ). Without further guidance from Congress, that would seem to encompass everything from frog ponds to the Mississippi river. Sorting out exactly which waterways are subject to these pollution safeguards has been the subject of redefinition and litigation ever since. The Supreme Court’s justices last considered the question back in 2006, and they too failed to muster a majority opinion. Writing for four of the nine, Antonin Scalia argued that federal authority extended only to “relatively permanent” waters. Writing for himself, Anthony Kennedy said that the rule should apply to waters that bear a “significant nexus” to navigable waters. Controlling precedent lies somewhere in the middle of these two nebulisms.

This is where we swam

Wading into the murkiness, the Obama administration issued a rule in 2015 that would clarify what counted as a water of the United States once and for all. It included wetlands and so-called ephemeral streams—those that flow only when it rains—on the theory that unregulated pollution of small tributaries will eventually accumulate in bigger bodies of water. The precarious health of the Chesapeake Bay and the “dead zone” of low oxygen spanning 9,000 square miles in the Gulf of Mexico are both caused by nutrient pollution of this sort. On December 11th the Environmental Protection Agency ( EPA ) announced that it would largely reverse the 2015 rule. The agency claims not to know how many streams and wetlands will be affected. But its own estimates, published a year earlier, suggest that protections would go for 18% of streams and 51% of wetlands.

Protecting wetlands has been a relatively bipartisan endeavour, at least at the federal level. Richard Nixon signed the original Clean Water Act. George H.W. Bush’s administration declared a goal of “no net loss” of wetlands. One-third of Americans get some of their drinking water from the streams being deregulated. “This would be the most significant weakening of Clean Water Act protections in its history,” says Jon Devine of the Natural Resources Defence Council, a lobby group.

For Mr Trump, the rollback completes a campaign pledge made to farmers, who objected vociferously to the Obama-era regulation. Organisations like the Farm Bureau, another lobby group, whipped up fears of government asserting authority over ditches and ponds. In truth both the regulation and the original law already contain generous carve-outs for farmers, says Caitlin McCoy, a fellow at Harvard Law School.

The EPA ’s professed rationale for the change is to provide regularity clarity and certainty. A look at its other recent actions suggest that the real aim is to please regulated industries. The agency pushed for rules allowing coal-power plants to resume dumping wastewater contaminated with mercury, arsenic and lead into streams and rivers. It has relaxed rules governing the disposal of coal ash—the toxic by-product of combustion that can leach into streams. And it is doing all it can to rehabilitate the struggling coal industry, which retains a political heft out of proportion to its economic value.

Because people admire Jeffersonian yeomen, farmers are frequently invoked by those keen on overturning environmental rules. Pinheaded bureaucrats insisting on permits for irrigation ditches offends what remains of America’s sense of rugged individualism. But other groups also stand to benefit from diminished water protections: mining companies, factories and chemical processors are keen to see the Obama-era rule disappear. Property developers and golf-course owners often have their plans stymied by wetland protections (why Mr Trump might be sensitive to their plight remains a mystery). Fore!