Sea mines and unexploded ordnance in navigational warnings

Moored mines can break loose in storms and drift. Since 2022 the Black Sea has produced a series of warnings about mines sighted or neutralised along its western and southern coasts, alongside large hazardous-operation areas off Ukraine that have been in force without an end date.

A mine warning gives the position where a mine was seen or destroyed. The position describes the sighting, not where the mine is now, and a warning's cancellation does not declare an area clear.

Mines also appear in war-risk advisories — notices about threats to merchant shipping in a conflict area — which seahazards files under war risk rather than as mine warnings, so a sea's mine count and its security situation are read separately.

Far more common are warnings about unexploded ordnance on the seabed: bombs, shells, mines and torpedoes from both World Wars and later conflicts, found by fishermen, dredgers, cable ships and wind-farm builders. Parts of the Baltic, the North Sea and the approaches to many ports were used as dumping grounds after 1945.

These warnings typically announce a find with a keep-clear radius, then a disposal operation — often a controlled underwater detonation — and then a cancellation. The cancellation ends the notice about that object only.

Navies also practise finding and clearing mines, and multinational clearance operations recover or destroy wartime munitions in European waters most years. Those exercises and operations are announced like any other activity: an area, a period, and a request to keep clear. Some exercise warnings mention practice mines — inert shapes laid for training — which are not a hazard of the same kind but are still to be avoided.

Mine and ordnance warnings are where the gap between a notice and the situation matters most. The archive can show how often explosives were reported in an area and how long the notices stayed in force. It cannot show how many remain, and an absence of warnings is not evidence of a clear seabed.