A prison worker at Hindley has been released by police probing the supply of drugs at the jail.
Detectives detained a woman in her 30s on Tuesday, on suspicion of supplying class A and class B drugs.
She was also being investigated for misconduct in a public office at the Bickershaw establishment.
Part of a joint probe between the North West Regional Organised Crime Unit and HM Prison and Probation Service, a house in Golborne was raided and a car was also searched.
A Greater Manchester Police spokesman confirmed the woman has been released under investigation after being questioned.
Detectives say the arrest followed a three-month long inquiry into prisons corruption, which is still ongoing.