Police have urged the public to stay away from Rivington reservoir after "grenade-type" objects were found at the site.
The area has been taped off since 8am this morning as police investigate.
The beauty spot, located near Bolton, was expecting a number of visitors ahead of the Easter holidays.
A Lancashire Police spokesperson said: "We are currently an incident at Rivington after a member of the public found what are suspected to be two grenade type devices."
They added: "There is a cordon in place at the moment and we would ask you to stay away from the area for now while we deal with the situation. We will update you further when we can."
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