Correction: An earlier version of this column incorrectly said that the Potomac made the advocacy group American Rivers’ list of endangered rivers for the first time in 2012. It was also listed in 1997 and 1998. The incorrect information came from American Rivers. This version has been corrected.

Just because you’re promoting a worthy cause doesn’t justify distorting the truth.

That’s a principle violated in Washington perhaps more than anywhere, most recently in an attention-grabbing report by an environmentalist organization declaring the Potomac to be “America’s #1 Most Endangered River.”

The top ranking wasn’t based on pollution levels or other scientific data. It wasn’t warranted by trends or policy changes that threaten our river more than any other. It isn’t as if the Potomac has been gradually creeping up the roster and finally reached the peak. This was the river’s third appearance since the annual list began in 1986.

No, the advocacy group American Rivers highlighted the Potomac this year primarily for slick political and public-relations motives. The group picked what it called “the nation’s river” in order to rouse citizens to fight efforts in Congress to weaken the Clean Water Act on the law’s 40th anniversary. It helped that it’s an election year, when Washington is in the news.

The strategy worked. Officials with American Rivers were pleased when local radio, television and newspaper reports gave the story a good ride. Most coverage omitted or buried that pesky detail that the No. 1 ranking was essentially a subjective judgment by a group with an agenda.

Public-relations experts faulted both American Rivers for hyping the story and the media for being too ready to bite.

“The number one ranking implies that the Potomac is worse than everything else. How is that not a lie?” said Paul Argenti, a corporate communication professor at Dartmouth.

“You have to have some sort of measurable justification when you do a ranking,” he said.

Kent Holland, a partner at the Plesser Holland public-relations firm in Washington, criticized American Rivers for being “disingenuous” but added, “The other side of the question is, where’s the skepticism from the Fourth Estate?”

Now, here are two important caveats. First, I am 100 percent behind American Rivers’ mission to reduce pollution in U.S. waterways. For the sake of all our region’s rivers, plus the Chesapeake Bay, I share the group’s concern about proposals that would cripple the Environmental Protection Agency.

Second, the Potomac is unquestionably at risk. Pollution washing off farms upstream remains a major problem. The river also faces a growing threat from dirty runoff from roads and other pavement in steadily expanding suburbs and urban areas.

Scientists still don’t fully understand how chemicals in the Potomac are causing male fish to start turning female, or what exactly that means for humans. Without improved controls, four decades of real progress could be reversed and imperil the source for drinking water for 5 million people.

Nonetheless, it was still maddening that nothing of substance in the American Rivers report justified proclaiming on its Web site that the Potomac is more “endangered” than every other U.S. river. Its announcement offered a fuzzy explanation that the Potomac’s problems are “emblematic of what’s at stake for rivers nationwide.”

Consider this: One of the report’s few specifics was a reference to the Potomac’s recent “D” grade for ecosystem health from EcoCheck, a partnership between scientists from the University of Maryland and the National Oceanic and Atmospheric Administration.

But the same study gave lower grades to four other waterways in our region, including “F’s” for both the Patuxent and Elizabeth rivers.

American Rivers officials acknowledged in interviews that the ranking isn’t strictly objective and relies in part on political criteria.

“Any time you have a list, whether it’s the top 10 movies of the year or the top 10 endangered rivers, there’s always some subjective judgment applied,” said Bob Irvin, the group’s president. “If our list were solely a list of what does the chemistry tell us is the most polluted river in the country, that probably would not change from year to year.”

Indeed, the “Top 10” are new almost every year — helping to attract media attention and gin up donations in a new set of media markets each time. Last year’s No. 1, the Susquehanna, was picked to highlight the threat posed by the natural-gas mining technology known commonly as “fracking.” Hydraulic fracturing is still around, but the Susquehanna didn’t make this year’s list.

American Rivers’ misrepresentation risks hurting the authority and believability of the green movement as a whole. Many other environmental organizations are rigorous about using scientific research to back up their reports.

“This is exactly what [nonprofit] organizations like theirs accuse corporations of doing. When you start acting like this, you lose credibility with people who are trying to do the right thing,” Argenti said.

Since I’m partly faulting my own profession here, I ought to mention that The Washington Post handled the story responsibly. The headline didn’t mention the No. 1 ranking, and the sixth paragraph noted that critics said there was “no scientific basis” to judge one large American river as more endangered than another.

Still, when next year’s report comes out, maybe we ought to ignore it.

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