The dogs in Dzerzhinsk are looking more like Smurfs than canines.

If you've been on Pet Internet this week, you've probably seen the blue dogs in the Russian town of Dzerzhinsk.

There was understandable worry about the pooches, but Reuters reports that the dogs are in "normal" condition at a local clinic. So what caused the stray dogs to turn blue? We don't for sure, but there's a good chance it was because of a very normal dog behavior: rolling in something they shouldn't have. 

Russian blue dog stands in snow
Credit: Priya Balu / Instagram

Here's the hypothesis of Paul Amerling, DVM, who has 25 years of clinical experience: There's an abandoned chemical plant near Dzerzhinsk, which, according to one Russian official, still may contain copper sulfate. Take a look at what that can look like when it's ground into a powder. Seems pretty similar to the dogs' new color, no? Maybe they just rolled in it. That would explain how their hair looks. 

"The dogs are sort of patchy blue," says Amerling, who has never seen blue dogs in his decades of animal medicine. "Certainly not uniform."   

The stray dogs probably didn't turn blue from eating the copper sulfate either, he says. He even contacted his former toxicology professor, who told him that ingesting too much copper can only make fur darker—not turn it blue.

Now, the dogs eating the copper sulfate would still be problematic because excessive copper can also damage a dog's liver and digestive system and maybe result in death. So it's no surprise Humane Society International's Vice President Kelly O'Meara, who spoke with Newsweek, is worried about the dogs.  

"The dye on their fur implies they have had direct contact with or even ingestion of potentially toxic or harmful substances. This could result in painful skin burning or itching or internal bleeding and illness that could lead to death, without veterinary intervention," she said.

A spokesperson for the Russian government told the country's media that officials are in talks to find the sources of the blue coloring and make sure all the dogs are OK.