Police handcuffed three teenagers Thursday evening for attempting to selling water without a permit on the National Mall.

Photos tweeted by passerby Tim Krepp, a tour guide and writer, show three plainclothes U.S. Park Police officers detaining the three African-American teens near the Mall's Smithsonian Castle, located between the Washington Monument and the U.S. Capitol.

The photos, which show the contraband in a plastic bin, were retweeted more than 7,000 times as of Friday morning.

"My kids sell water and everyone smiles at them. These kids do it and get arrested. It IS racist," Krepp tweeted. In another tweet, he wrote: "God forbid the actual free market be allowed on our National Mall."

A spokeswoman for the U.S. Park Police, Sgt. Anna Rose, confirms three teenagers were detained for vending without a permit, but says she feels "this has gotten blown out of proportion."

The three teens, ages 16 and 17, were detained for "illegally selling water" but were not charged, Rose says. They were held until their parents arrived. A fourth individual was immediately released after officers determined he was uninvolved, she says.

It's not immediately clear if the teens were taken to the police station or if they waited for their parents on the Mall. It's also unclear how long they waited.

But Rose says "this was not some hours-long ordeal."

Rose says that although the officers were not wearing uniforms, "there was no sting operation" or concerted crackdown on drink-sellers. She could not comment on why officers decided not to charge the teens with a crime, but says officers have discretion to make such decisions.

The National Park Service requires vendors on the Mall to be permitted, meaning most people risk legal consequences if they sell drinks to tourists on sweltering days.

"Vending on the National Mall is illegal without a permit," Rose says. "The National Park Service has a whole office dedicated to permitting."

Update 6/24/17: After publication of this article, a former D.C. resident asked the National Park Service how they could acquire a permit to "sell water on the National Mall on especially hot days." They were told that's not possible.

Elizabeth Buchanan, event compliance monitor for the National Mall, said in an emailed response:

Unfortunately we cannot issue permits for selling water or any other food or beverage items. Guest Services Incorporated holds the contract with The National Park Service to operate the existing food/beverage stands within the park. Any other vending of food/beverages would be an infringement on their contract. I'll include a link to the DC Permits office. You may want to contact them to see about the streets in the surrounding area that are not under the jurisdiction of the National Park Service.

Thanks