I want to know the answer to the following question:
What river is a tributary of the River Thames?
All the background I'm provided with is that "Access to canals and rivers has improved recently, including the creation of the Thames Path, some 28 miles (45 km) of which is within Greater London, and The Wandle Trail; this runs 12 miles (19 km) through South London along the River Wandle, a tributary of the River Thames.". Is that enough to answer the question?
Answer: yes