Officers from the Special Group for Underwater Activities, or GEAS, have found 7 explosive devices in Balearic waters this year, 2 in Majorca and 5 in Minorca.
The devices are usually mortar shells or aviation bombs and are often spotted by swimmers or people practicing water sports.
When the Guardia Civil is notified about a device, the GEAS tracks its exact location.
Last week a mortar grenade was discovered 3-metres below the surface in the sa Mola area of Minorca.
Anyone who spots one of these devices is advised not to touch it and to call 062 immediately.