Police seized drugs and arrested a woman in a Carpenders Park dawn raid.
Officers carried out a warrant at an address in Romilly Drive at 5.37am on Tuesday, March 5.
They confiscated drugs and arrested a 52-year-old woman from Watford on suspicion of being concerned in the supply of cannabis.
The amount seized and approximate value is not currently known, and the suspect has been released on bail while enquiries continue.
Residents had reported seeing "lots of police cars lining the street" before the force confirmed the details this afternoon.
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In a separate incident, a 28-year-old man admitted producing Class B drugs with intent to supply at a property in nearby South Oxhey.
Endrit Pepkolaj, of no fixed address, pleaded guilty at St Albans Crown Court on March 6 after police raided the "large-scale" cannabis farm in Gosforth Lane on February 1.
They discovered a total of 168 plants, estimated to be worth at least £47,000, along with the defendant.
He has now been remanded in custody ahead of sentencing on March 20.
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