In a profile of Tucker Carlson published in the Atlantic Sunday, the right-wing Fox News host points his finger at a lot of things: the leadership class, America’s “obsession with race,” and immigrants, who he claims are responsible for making the Potomac River “dirtier and dirtier and dirtier and dirtier.”

What might possess a person to make such a statement, you ask? Writer Elaina Plott prodded Carlson about similar racist comments he’s made about immigrants in the past—in particular, that they make America “poorer and dirtier and more divided.” (Some companies pulled ads from Carlson’s show after that).

By way of explanation, Carlson doubled down on his remarks:

“I hate litter,” he said. For 35 years now, he said, he has fished in the Potomac River, and “it has gotten dirtier and dirtier and dirtier and dirtier. I go down there and that litter is left almost exclusively by immigrants, who I’m sure are good people, but nobody in our country—”

“Wait,” I said, cutting him off, “how do you know they’re—”

“Because I’m there,” he said. “I watch it.”

On Monday, Hedrick Belin, president of nonprofit land trust Potomac Conservancy, published a response to Carlson’s “dirtier” rant that basically said: “Uhm, what?”

No, @TuckerCarlson, immigrants don't make the Potomac dirtier. Here's our response to your groundless comments made in @TheAtlantic https://t.co/lITqiunSIO@elainaplott

— Potomac Conservancy (@TheNationsRiver) December 16, 2019

Belin and his colleagues felt “compelled to respond to this groundless accusation not just because it’s factually incorrect, but because it’s racist plain and simple,” the statement said.

The conservancy points out that the Potomac River is not, by any stretch of the imagination, getting dirtier. It’s in fact getting much cleaner. The conservancy rates the river a B on its Potomac Report Card, a huge step up from its D+ grade in 2007.

Also, Belin points out, litter isn’t the worst source of water pollution. “Agricultural runoff is the number one contributor of excess nutrients and sediment found in our waterways, but urban polluted runoff may soon replace it as the top contributor,” he wrote.

And, in case it’s not obvious, no one community is responsible for polluting the river. “To make the egregious assertion that one group over another is at sole fault for the river’s woes is wildly inappropriate and doesn’t reflect the true nature of local pollution sources,” Belin wrote.

The Atlantic notes that, according to Nielsen, Carlson’s show averages 3.4 million viewers nightly, successful by anyone’s measure (and utterly trouncing his competition at other large networks). But over the years, Carlson, who formerly hosted shows on MSNBC and CNN, has increasingly spouted anti-immigrant and other racist views on his program, drawing praise from neo-Nazis and white supremacists. Carlson maintains that he is not racist and does not support racists.

Plott writes that Carlson measures his success by “how many people in Washington think he’s wrong.”

By that measure, Belin might argue that the Fox News pundit is very successful. “There’s a time to speak truth against ignorance and to stand up for our values,” Belin said. “And that time is now.”