Yaman Akdeniz, a law professor, turned by habit to Wikipedia to find out when the latest “House of Cards” season was released.
“You forget that it’s blocked, and then you click on it and then — boomph, nothing: You realize you can’t access it,” said Professor Akdeniz, describing his personal form of digital whiplash. Many people didn’t realize until after it was blocked, he said, that Wikipedia “was so much a part of our lives.”
Mr. Dede said he mourned the loss of “part of your memory.” Even in his academic world, where Wikipedia is sometimes scorned, the website was secretly seen as a good starting place for research, he said.
But beyond the problems it has created for the curious, Turkey’s Wikipedia ban is a reminder of something darker, government critics say: a wholesale crackdown on free expression and access to information, amid wider oppression of most forms of opposition.
Wikipedia is just one of 127,000 websites blocked in Turkey, estimated Professor Akdeniz, who has led legal challenges against the Wikipedia ban and other web restrictions. An additional 95,000 pages, like social media accounts, blog posts and articles, are blocked on websites that are not otherwise restricted, Mr. Akdeniz said.
Some of these sites are pornographic. But many contain information and reporting that the government finds embarrassing. Sendika, an independent news outlet, is now on the 45th iteration of its website. The previous 44 were blocked.
The coup attempt gave President Recep Tayyip Erdogan the political cover to expand a crackdown on his opponents, including in the traditional news media. Since the coup, 190 news organizations have been banned and at least 120 journalists jailed.
“The international community noticed this issue by reference to the Wikipedia block, but it’s not a new thing from our point of view,” Mr. Akdeniz said. “Critical media is under stress on a daily basis — and what made that visible is the Wikipedia ban.”
For students, the ban could not have come at a worse time: just as they were knuckling down for exams.
“It’s a big obstacle,” said Ege, a 17-year-old high school student, whose surname has been withheld at the wishes of his headmaster. “Wikipedia is the source of the sources — you can find everything there.”
While studying Jean Anouilh’s French adaptation of a Greek tragedy, “Antigone,” Ege’s friends had wanted to know more about the heroine’s father: the mythical King Oedipus, who mistakenly married his mother.
“The Oedipus bloodline, what he did, the curse that was put on his family,” Ege’s classmate Yusuf said. “Reaching that information wasn’t exactly easy.”
Wikipedia use has fallen by 85 percent in Turkey since April, but some have managed to circumvent the ban with a VPN, or virtual private network, a tool that helps web users gain access to blocked websites.
According to GlobalWebIndex, a group that researches worldwide internet activity, Turkey has the third-highest VPN prevalence in the world. More than 45 percent of Turks ages 16 to 64 who have web access used a VPN in the first quarter of 2017, and the practice has become second nature even for some beginners.
“My mom learned to send an email two years ago,” Mr. Dede said. “The next thing, she’s learning how to access a VPN.”
But VPN use comes with an unwelcome side effect. Because Wikipedia does not allow VPN users to edit articles, Turks are unable to correct or update information posted on the site or write new articles.
“Turkey has lost its voice online because of its inability to edit Wikipedia,” said Alp Toker, a co-founder of Turkey Blocks, a group that tracks Turkish internet censorship.
In addition, some VPNs are also banned. Those that remain are often slow, particularly on cellphones, so using one is sometimes not worth the hassle.
As a result, some students are getting desperate about their final exams.
“Dear President of the Republic, the Leader, open up Wikipedia at least until the end of the finals week,” one wrote on Twitter. “President, I am overwhelmed, hear me out.”