The question dates to the crafting of the 1972 Clean Water Act: Which waters, precisely, are considered the “waters of the United States” and thus deserve regulatory protection? The law directs the Environmental Protection Agency and the U.S. Army Corps of Engineers to come up with an answer. And they did in 2015, arriving at a much-needed clarity after decades of uncertainty, fueled, in part, by two Supreme Court rulings. The work of the agency and the corps was driven by science (some 1,200 peer-reviewed studies) and input from assorted stakeholders.

Not everyone agreed with the answer. Farmers and rural landowners voiced loud opposition, winning the current hold in the courts, and then they gained an ally in the White House. A month into his administration, President Trump gave his appointees the task of rolling back the “waters” rule, which he called a “disaster” and “a massive power grab.” On Tuesday, they delivered.

The proposed rule amounts to an unfortunate retreat, one that departs from the purpose of the Clean Water Act. It neglects the connections among waterways. Even pollution flowing into smaller streams makes large bodies of water vulnerable. That is what the science shows.

Consider that in the late 1980s, President George H.W. Bush advocated no net loss of wetlands. He understood the indispensable role wetlands play, absorbing flood waters, filtering impurities, providing wildlife habitats. Ohio has lost 90 percent of its wetlands.The proposed rule would cover wetlands with a “continuous surface connection” to lakes, rivers and streams, leaving at least half of current wetlands without regulatory protection.

The proposed rule also narrows the protection for “ephemeral” streams, in which water runs only during or after rainfall or snowfall. Look at such streams when they are dry, and it may seem sensible to skip regulation. Yet when they do run, they flow to larger bodies of water. Consider that they account for 18 percent of all streams nationwide, and about one-third in the arid west.

Add “intermittent” streams, which could be open to losing regulatory protection, and the two categories provide drinking water to an estimated 117 million Americans.

The president and other critics insist the new rule is necessary to curb the regulation of “every puddle” and “every ditch.” They exaggerate, to say the least. For instance, the concerns of farmers long have been part of the discussion. They have received relief in the past, and their interests were accommodated in the 2015 rule, which, in total, expanded the reach of the Clean Water Act by 3 percent.

It is worth bearing in mind, too, that the proposed rule runs against shared interests. It makes more difficult the task of reducing pollution in the Cuyahoga River and thus works to the detriment of the Cuyahoga Valley National Park. It clashes with the objectives of the Great Lakes Restoration Initiative, most notably, in neglecting tools to prevent runoff that feeds harmful algal blooms in Lake Erie.

One aspect of the regulatory process is that rules cannot be replaced at a whim or just to serve an agenda. The proposed rule must be backed by sufficient scientific evidence and legal arguments to show compliance with the Clean Water Act. So expect court battles if the rule takes effect as written after the current public comment period. The fight is worth waging. The regulation of wetlands and smaller streams is crucial to protecting this region's and the country’s waters.