The suspicious device was discovered in the Town Gardens, known locally as the Blind Gardens, which border St George’s Way, Cutty’s Lane and Silam Road, by contractors who were dredging the pond at around 10.30am.
Police were soon on the scene and established an exclusion zone of 100 metres around the device, which was found partially submerged in the mud and left in situ.
Explosive Ordnance Disposal teams from the RAF had been called out to the park to try and establish what the suspicious object was.
As a precaution, the southbound carriage way of St George’s Way between Six Hills and Fairlands Way was closed to traffic.
A nearby shopkeeper said: "The first I knew of something happening in the gardens was when I walked up past there after parking my car.
All I know is that they are refurbishing the park, and there was a rumour going around they might have found a bomb."
The Town Gardens are undergoing an extensive renovation project at the moment by Green Heart Partnership and HTA Landscape Design, who have been appointed by Stevenage Council to redesign the 3.85 hectare gardens.
The gardens were conceived as part of the New Town development in the 1960s, but have fallen into decline and are generally perceived as neglected and unsafe.
A police spokeswoman said that no one has been evacuated from their homes and nearby businesses were operating as usual as the potentially-lethal device was being investigated.
