GEOFF BENNETT: The U.S. Supreme Court has again weakened the authority of the Environmental Protection Agency.

As William Brangham reports, today's ruling limits the agency's power to curb water pollution.

WILLIAM BRANGHAM: Geoff, this case goes back 15 years, when the EPA, citing the landmark Clean Water Act, blocked in Idaho couple from building a house on their property because there was a wetland on it, and the property was next to a big lake.

All nine justices agreed the EPA didn't have the authority to regulate these homeowners' property, but there was stark disagreement over how to determine when a body of water can and should be protected.

To understand the implications of this ruling, we are joined again by Coral Davenport.

She covers energy and environment for The New York Times.

Nice to see you again.

CORAL DAVENPORT, The New York Times: Great to be here.

WILLIAM BRANGHAM: So, this was a unanimous ruling by the court that, in this Idaho case, the EPA had overstepped.

But the majority went much farther and went really a much deeper cut into the EPA's authority.

What did they rule?

CORAL DAVENPORT: Essentially, they said that the EPA, which, until yesterday, had the authority to regulate most of the wetlands in the United States to protect the wetlands and to punish anyone who had polluted them, sharply limited or sharply reduced the amount of wetlands that would be subject to federal protection.

It said, in order for a wetland to be subject to some -- any kind of federal protection regulation, it has to directly join up to or be connected to a larger body of water.

That might sound sort of obscure, but that decision really cuts out millions of acres, probably more than half the wetlands in the United States, from federal protection.

WILLIAM BRANGHAM: Can you remind us, for people who think of wetlands as sort of swampy areas that are not that -- who knows what they really do -- why we care about wetlands?

CORAL DAVENPORT: Absolutely.

So a wetland might not be a place that you want to visit.

You're right.

A lot of wetlands literally do fall into the definition of swamp or bog or soggy area.

Wetlands are important for two reasons.

One, they're a major source for biodiversity.

Many, many species make their home in wetlands.

And if the wetlands are polluted or not subject to any kind of environmental protection, you might risk losing a lot of that biodiversity.

Wetlands protect humans to.

Wetlands are a really important source for protection from floods.

And so, if they dry up, if they are filled in, if they disappear, this -- they're a buffer for flooding.

And that is a role that they play that is becoming a lot more important now in the era of climate change, where we're experiencing a lot more flooding.

So wetlands... WILLIAM BRANGHAM: Yes, we need more land to suck up all that water that's falling.

CORAL DAVENPORT: Exactly.

Exactly.

So those are sort of the roles that wetlands play.

And that's kind of why the Clean Water Act had envisioned federal protection for wetlands.

WILLIAM BRANGHAM: So who is cheering this ruling today?

Obviously, this Idaho couple is, but who else is going to be heartened that the EPA can't regulate wetlands as effectively?

CORAL DAVENPORT: Sure.

So there were a lot of groups that had been pushing legally and politically for the overturn of these regulations and these protections, chiefly farmers, real estate developers, golf course developers.

Not surprisingly, former President Trump had pushed really hard to roll back a lot of these regulations, because they really did get in the way of what a lot of people could potentially do with their land.

And so, without these protections, it really takes away -- it takes away penalties for filling in wetlands and developing.

It takes away penalties for farmers who could have been penalized for using fertilizers or pollutants that would run into wetlands, and they would receive penalties from the EPA.

So a lot of those areas that had been protected, now that the protections are gone, those are the groups that are saying, well, now we can -- we can do what we want with this land.

WILLIAM BRANGHAM: President Biden today in a statement that was very critical of this ruling said that he's going to try to redouble efforts to get states, localities and tribes to step up their enforcement of water protections.

How likely is that to make a difference in -- to sort of step into this breach.

CORAL DAVENPORT: So now that this federal protection has been lifted for so many millions of acres of wetlands, a lot of these areas, at this moment, have literally no legal protection whatsoever from pollution.

It absolutely is possible that states could step in and write new state laws or rules to protect the wetlands.

But, in fact, more than 20 states already have statutes in place that say the state rules cannot be more stringent than the federal rules.

So if we were to see that happen, it would probably only happen in about in about half the states, if at all.

So that - - President Biden made that call.

Legally, it's harder to see how that would happen in about half the country.

WILLIAM BRANGHAM: Coral Davenport of The New York Times, thank you so much.

CORAL DAVENPORT: Always happy to be here.