If you know what fracking is, you’re worried — but most New Yorkers haven’t a clue.

A new poll found that 59 percent of city residents who were aware of the controversial natural-gas drilling process are “very concerned” about its effect on the water supply and another 31 percent are “somewhat concerned.”

But nearly two-thirds of the 408 New Yorkers questioned said they hadn’t heard of fracking before the pollster asked about it, according to the Civil Society Institute, a think tank involved in environmental issues that sponsored the survey.

Fracking, or hydraulic fracturing, involves fracturing rock to stimulate wells. Critics say it can poison drinking water, but energy industry officials say there’s no proof of that.