Merseyside Police says a handgun and ammunition have been recovered from a lake near Arrowe Park Hospital.
A member of the public found ammunition in Arrowe Brook at around 2.35pm on 19 November, and following an underwater search conducted by The North West Underwater Search Unit, a pistol was recovered.
The gun, ammunition and a magazine have been taken for forensic examination to establish if there are any links to any offenders or incidents.
Inspector Chris Lucan-Pratt said: “Offenders who carry and store weapons often go to great lengths to try to conceal firearms and knives, or dispose of them in an attempt to evade justice.
“But Merseyside Police conducts regular warrants and searches of land targeting those places and individuals involved in the storing of firearms, and regularly takes them out of circulation.
“Information from the public who have found weapons or believe they know where they may be stored is also absolutely vital part of those efforts to take them out of the hands of criminals.
“Every single time a weapon is taken out of circulation it is good news for the people of Merseyside.
“They are used by criminals to cause serious harm, so when members of the public come to us with information about where they may be stored they are doing their communities a great service and we will always act.”