Adrienne Keene, a Cherokee writer who created the Native Appropriations online forum, wrote in a blog post that Rowling's take recklessly misrepresents a tradition that still has very real meaning to many.
The belief in skin walkers "has a deep and powerful place in Navajo understandings of the world," Keene wrote. "It is connected to many other concepts and many other ceremonial understandings and lifeways. It is not just a scary story."
But that history and nuance could be eclipsed by Rowling's take, Keene said. "Rowling is completely re-writing these traditions. Traditions that come from a particular context, place, understanding, and truth. These things are not 'misunderstood wizards.' Not by any stretch of the imagination."
Keene also took her objections to Twitter, where Rowling has been responding to fans with questions about the various minutiae of wizard history. In a reply to one Twitter user, who wanted to know if skin walkers were good or bad, Rowling wrote that the legend was fabricated by people without magic.
Keene jumped in with her own sharp Twitter reply:
"It's not 'your' world. It's our (real) Native world. And skin walker stories have context, roots, and reality."
"You can't just claim and take a living tradition of a marginalized people. That's straight up colonialism/appropriation @jk_rowling."
Keene was not alone. Other Native people took to Twitter to voice their disappointment and demand a response from Rowling, who has not answered her detractors online. A Pottermore spokesperson declined to comment for this story.
Navajo writer Brian Young tweeted that Rowling's depiction of Native culture left him "broken-hearted":
"Yo, @jk_rowling my ancestors didn't survive coloniSation so you could use our culture as a convenient prop."
Some Native American fans also objected to Rowling's use of the phrase "the Native American community" - there are hundreds of different Native American tribes, each with their own culture and traditions - as well as references to certain stereotypes. Rowling writes that the Native American wizards were "particularly gifted in animal and plant magic"; the trailer for the series features a Native man in a loincloth leaps from a cliff and turns into an eagle.
Johnnie Jae, founder of the radio show and website A Tribe Called Geek, bemoaned that Rowling would likely be applauded for including Native culture in her fictional history - rather than questioned for the way that culture was portrayed.
Sure enough, several Potter fans came to Rowling's defense on Twitter, arguing that she intended to honour Native culture, that the story is "just fiction" and that her critics were being oversensitive.
But the mass appeal of Harry Potter is exactly why Native voices needed to speak up, Keene wrote.
"As I often say, when you're invisible, every representation matters," she said. "And the weight and impact of the Harry Potter brand can't be ignored."