The department posted a photo to Twitter of the grimy sphere, which turned out to be nothing more than an oversized a holiday decoration.
"Luckily, upon closer inspection, it is a giant glittery Christmas bauble!" police said.
The bulb still had its hanging loop attached. Authorities did not say how the decoration ended up alongside the river.
The Met's Hackney Bureau remarked the discovery was a "wapping great bauble."
"Fortunately not as given, but shows as our training teaches us 'expect the unexpected,'" police said.
The incident happened nearly a week after a World War II bomb was discovered at a construction site in Kingston-upon-Thames.
The incident on Thursday forced students at Kingston University to be evacuated until Sunday.