THE bomb disposal team closed off a beach after a dog walker picked up a hand grenade thinking it was a stone.
The Colchester unit were called to Dovercourt beach for a second time on Sunday after the dog walker raised the alarm.
The walker, who did not have her phone, called to her neighbour whose son is an Army explosive expert.
The off duty expert arrived at the beach and quickly set up his own 30 metre cordon until the police, coastguard and army unit arrived.
They had already been called to the beach the day before when another hand grenade was found.
Essex Police have now put out a warning saying five grenades have been found in the past five weeks.
They were found on the beach near West End Lane and The Promenade and three were found near Lower Marine Parade on Saturday July 12.
Insp Paul Butcher said: "It would appear that the grenades might have been in a crate that ended up in the sea during the Second World War. That crate might be breaking up or has been disturbed by dredging in the port and has resulted in these five devices being washed ashore along the same stretch of beach.
"We are asking people to be vigilant if visiting this beach and to dial 999 if they find any of these devices. Some of them have been covered in barnacles but the one yesterday looked almost as new despite being in the sea, possibly for many years.
"Anyone who finds a grenade should not touch it or move it but should call police immediately.”