You'd much rather not encounter an explosive in your nets or on board but when it does happen, this chart of explosives may come in handy.
It is not always easy to see whether you are dealing with an explosive or not. In time it may have changed shape, it may be covered with mud or algae or it can be that you have found only a part of the explosive.
When in doubt, it is best to assume it is indeed an explosive. Alert the MRCCC (Maritime Rescue and Coordination Centre) at once. They will ensure the necessary assistance is provided.
A good description always helps.
Take pictures of the explosive and send them to firstname.lastname@example.org. Should that not be possible, describe the explosive as accurate as you can to the MRCC's operator. Use the explosives chart for this. It features the explosives most commonly found in the North Sea and gives you an idea of their shape and size.
You'll also find recommendations on what (not) to do until the mine-hunting unit arrives.
More information can be found in Notices to Mariners n°1.