What is thought to be a submarine or boat has been identified submerged in Lough Foyle.
The North's Environment Minister Alex Attwood has said he had viewed sonar images of the vessel.
Urgent work is now to be undertaken to determine how and when the submarine or boat came to rest in the lough.
The Minister said there appears to be no record of the vessel going missing.
He said it was crucial that no diving should occur in the vicinity of the vessel.