They want dirty water. “Restore dirty water!” they cry.

President Trump is expected to sign an executive order on Tuesday aimed at rolling back one of former President Barack Obama’s major environmental regulations to protect American waterways, but it will have almost no immediate legal effect, according to two people familiar with the White House plans.

The order will essentially give Mr. Trump a megaphone to direct his new Environmental Protection Agency administrator, Scott Pruitt, to begin the complicated legal process of rewriting the sweeping 2015 rule known as Waters of the United States. But that effort could take longer than a single presidential term, legal experts said.

But at least they’re getting started on doing away with that pesky clean water that nobody wants.

Mr. Pruitt, who was confirmed by the Senate to his new position this month, is expected to enthusiastically dive in to the lengthy task of undoing major environmental rules on clean water, climate change and air pollution. In his former job as attorney general of Oklahoma, Mr. Pruitt led or took part in 14 lawsuits intended to block the E.P.A.’s major regulations, including the clean water and climate rules that he is now charged with dismantling.

Speaking over the weekend at the Conservative Political Action Conference, Mr. Pruitt told an audience, to applause, “I think there are some regulations that in the near term need to be rolled back in a very aggressive way,” and he said those rollbacks would probably begin this week.

The clean water rule, completed by the Obama administration in spring 2015, was issued under the 1972 Clean Water Act. It gives the federal government broad authority to limit pollution in major bodies of water, like Chesapeake Bay, the Mississippi River and Puget Sound, as well as in streams and wetlands that drain into those larger waters.

A stirring ambition, undoing all that.

The Obama administration’s water rule, put forth jointly by the E.P.A. and the Army Corps of Engineers, was intended to clarify that authority, allowing the government to once again limit pollution in those smaller bodies of water. Environmentalists have praised the rule, calling it an important step that will lead to significantly cleaner natural bodies of water and healthier drinking water.

But it has come under fierce attack from farmers, property developers, fertilizer and pesticide makers, oil and gas producers, golf-course owners and other business interests that contend that it will stifle economic growth and intrude on property owners’ rights.

Well you can see their point. Rivers and streams are so handy for sluicing away agricultural runoff, pesticides, motor oil – you name it, rivers whisk it away.