In the tangled reeds a letter is deleted! (6)
I believe the answer is:
erased
'is deleted' is the definition.
(I've seen this before)
'in the tangled reeds a letter' is the wordplay.
'in' means one lot of letters goes inside another.
'the tangled' is an anagram indicator.
'a letter' becomes 'a'.
'reeds' is an anagram of 'ersed'.
'ersed' placed around 'a' is 'ERASED'.
(Other definitions for erased that I've seen before include "deleted material" , "'Wiped out, deleted (6)'" , "torn off" , "Removed by rubbing" , "Rubbed out, expunged" .)