Aquatic plant, deep down, tangled (8)

I believe the answer is:

pondweed

'aquatic plant' is the definition.
(pondweed is a kind of aquatic plant)

'deep down tangled' is the wordplay.
'tangled' indicates anagramming the letters.
'deep'+'down'='deepdown'
'deepdown' anagrammed gives 'PONDWEED'.

(Other definitions for pondweed that I've seen before include "Aquatic plant" , "water plant" .)

I've seen this clue in The Telegraph.

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