Thickening agent from Niagara (4)

I believe the answer is:

agar

'thickening agent' is the definition.
(I've seen this in another clue)

'from niagara' is the wordplay.
'from' indicates the answer is hidden within the clue.
'AGAR' is hidden in the letters of 'niagara'.

(Other definitions for agar that I've seen before include "Food-thickening jelly" , "contribution to culture?" , "Substance derived from seaweed" , "Seaweed jelly" , "found in the sea" .)

I've seen this clue in The Sun.

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