Sewer, lake and river back in northeast (6)
I believe the answer is:
needle
'sewer' is the definition.
(I've seen this before)
'lake and river back in northeast' is the wordplay.
'lake' becomes 'L' (geographical abbreviation).
'and' is a charade indicator (letters next to each other).
'river back' becomes 'eed' (I can't explain this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'northeast' becomes 'NE' (abbreviation).
'l' put after 'eed' is 'eedl'.
'eedl' placed inside 'ne' is 'NEEDLE'.
Can you help me to learn more?
(Other definitions for needle that I've seen before include "Part of gramophone" , "Pin" , "Provocation" , "Item for sewer" , "It's vital to baste" .)