Rivers don't have weather. Do you mean the weather in towns located by the River Thames?
It is variable but close to the general weather temperature.
That would be the River Thames.
The River Thames is the major river through London, cutting right through the middle of the city. There are many other rivers in London, such as the River Lee (or Lea) and the River Brent.
The river Thames (pronounced temz)
London is situated on the River Thames (pronounced 'temz'.
Thames River
The Thames flows through London.
The River Thames has multiple confluences. One such is the confluence of the River Thames and the River Darent at Dartford.
The river Thames.
The river Thames is in England.
River Thames.
They can be done at anytime but the weather will be warmer in the summer.