A water treatment plant in Florida was targeted by hackers who tried to poison a town’s water supply, according to the local sheriff.

An as yet unidentified suspect managed to get through a computer security system for the plant that serves the city of Oldsmar, Florida, on Friday, and tampered with the amount of chemicals in the water supply.

They briefly increased the amount of sodium hydroxide from 100 parts per million to 11,100 parts per million, Pinellas County Sheriff Bob Gualtieri said at a news conference on Monday.

The chemical is used to treat the acidity levels in the water supply, but is also a component in things like soaps and drain cleaners.

In high concentrations, it can cause irritation, burns and other complications.

Luckily, the change in the chemical levels was spotted by a supervisor, who then managed to reverse the increase.

The city, which is around 15 miles northwest of Tampa – which played host to the Super Bowl on Sunday night – and its 15,000 residents were not put at risk, officials added.

“At no time was there a significant adverse effect on the water being treated,” Mr Gualtieri said. “Importantly, the public was never in danger.”

The remote access system has been disabled since the incident, with officials saying there were other safeguards in place to prevent the increased chemical levels from getting in to the water.

Nearby city leaders were told of the incident and advised to check their systems.

According to the Tampa Bay Times, a worker at the plant first noticed the unusual activity at around 8am on Friday after someone accessed the system.

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They then took control at around 1.30pm, and manipulated the software that controls the water treatment and increased the amount of sodium hydroxide, The change was spotted and quickly reversed.

Investigators from the local county sheriff’s office, the FBI and the Secret Service said it is not yet clear where the attack came from.