Problem caused by stream with river further down (7)

I believe the answer is:

tickler

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'problem' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for tickler that I've seen before include "Difficult problem" , "puzzle" , "One catching trout by hand" , "trout farm employee?" , "Poser" .)

I've seen this clue in The Times.

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