Last of tents etc., blown away in river (3)

I believe the answer is:

cam

I'm a little stuck... Click here to teach me more about this clue!

'river' is the definition.
(river in Cambridge, England)

I don't understand the remainder of the clue.

(Other definitions for cam that I've seen before include "Part of engine" , "running into Great Ouse?" , "It controls the motion of engine cylinder valves" , "Projection on rotating cylinder" , "River; shaft projection" .)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app