Weddding rings and cameras could be uncovered as St James's Park is drained and cleaned.
Work started this week on cleaning and refilling the lake in St James's Park, to improve the water quality.
It was last drained in 1987, uncovering items resting on the bottom, including said rings, cameras and umbrellas.
St James's Park manager Mark Wasilewski said: "Silt, leaves and other materials have accumulated in the lake and we felt that this would be an appropriate opportunity to drain and clean it. I'm curious to see what turns up this time."
The lake will be emptied in two sections with a temporary dam built down the middle, so wildlife will have access to water and an island at all times.
When the water is drained, the silt will be removed and the condition of the base of the lake will be inspected and repaired if necessary.
The project is set to be completed by the end of April.
A Royal Parks spokeswoman said lost property would be handed to police, who will try to find the rightful owners.