The device on Sonning Bridge in Berkshire visually bears all the hallmarks of a regular cash machine, including a screen, buttons, and slots for bank cards and the dispensing of cash.
But it is adorned with Impro Solutions logos, indicating that a real bank is not behind the bridge's new look.
Impro is an artist behind a range of confounding previous installations on the bridge, including a phone, a postbox, and a door.
Other japes have included a large Google Maps pin at Playhatch Roundabout.
Regarding his latest work, he simply said: "Banks have reacted to complaints about branch closures and accessibility by opening cashpoints on river bridges for boaters within minutes of Keir Starmer walking into No 10.
"The first is on Sonning Bridge."
As yet there have been no sightings of other bridge cash machines.
A close up of the cash machine, which has a screen, buttons, slots for bank cards and the dispensing of cash, with Impro Solutions logos at the top and bottom
Little personal information is known about Impro, other than he lives in Oxfordshire.
In a rare interview with the BBC in 2014 he said his art was inspired by his belief that people are encouraged to take life seriously "despite the fact that it's absurd and tragic".
His postbox gag drew international attention when it caught the eye of famous spoonbender Uri Geller.
Mr Geller said: "I have never seen anything like this anywhere in the world. It's a new one on me."
He even suggested a possible culprit - the "ghost of a mischievous little girl" who had apparently been seen walking on the bridge.
