Footage shows the aquatic mammal bobbing up close to Twickenham Bridge.
Dolphins have been spotted in the river on a number of occasions, and back in 2017, a video emerged of them swimming close to Embankment Pier.
Pollution in the Thames has been under the spotlight in recent weeks after high levels of E.coli were found along a stretch of the water used for the historic boat race.
E. coli can cause a range of serious infections and other side-effects and rowers were told ahead of the race not to enter the river.
RIP dolphins.