Last to finish by river (6)
I believe the answer is:
endure
'last' is the definition.
(I know that last can be written as endure)
'finish by river' is the wordplay.
'finish' becomes 'end' (synonyms).
'by' means one lot of letters go next to another.
'river' becomes 'ure' (river in Yorkshire).
'end'+'ure'='ENDURE'
'to' acts as a link.
(Other definitions for endure that I've seen before include "Put up with something" , "Suffer, tolerate" , "Last or suffer patiently" , "Go through" , "Tolerate, put up with" .)