The medals were found on 4 May in a plastic bag secured under a brick
A Military Cross and five other World War II medals have been found next to the River Swale in Richmond.
The medals were discovered in a plastic bag along with a set of miniature replicas by a man walking by the river.
Police said the Military Cross was awarded to Lt Thomas Reynolds, service number 108199, of the King's Own Yorkshire Light Regiment.
His address was given as Hindhead in Surrey. Police are appealing for help to reunite the medals with their owner.
The Military Cross, which was awarded for gallantry, bears the inscription Lieutenant T Reynolds, KOYLI (King's Own Yorkshire Light Regiment), 22 April 1943.
The other medals include the 1939-1945 War Medal, the 1939-45 Defence Medal, the 1939-1945 Star, the North and North East Africa Star (1st Army) and the 1943-1945 Italy Star.
They are inscribed Major T Reynolds - KOYLI.
Sgt Neil Northend, of Richmond Police, said: "These sentimental and historically valuable medals are an unusual find and I am very keen to reunite them with their owner as soon as possible.
"Anyone who recognises the medals or can provide any information that could help us find the person that they belong to, please get in contact with the police as soon as possible."