A rogue actor remotely accessed a Florida city’s water treatment system and tried to poison it by increasing the lye concentration to over 100 times the normal amount, Pinellas County Sheriff Bob Gualtieri said Monday. The attack was thwarted before the water supply of Oldsmar—about 17 miles from Tampa—could be compromised, according to the sheriff. “Importantly, the public was never in danger,” he added.

According to Gualtieri, a treatment plant operator witnessed on-screen that someone remotely accessed the computer system, manually changing the lye concentration from 100 parts per million to 11,100 parts per million, which the operator immediately reversed. Law enforcement is currently investigating the matter. “If you put that amount of that substance into the drinking water, it’s not a good thing,” Gualtieri said.