Bleat lacking energy by worker, that's obvious (7)
I believe the answer is:
blatant
'obvious' is the definition.
(I've seen this before)
'bleat lacking energy by worker' is the wordplay.
'lacking' indicates named letters should be taken away.
'energy' becomes 'e' (physics symbol as in E=mc2).
'by' means one lot of letters go next to another.
'worker' becomes 'ant' (worker is a type of ant).
'bleat' with 'e' taken away is 'blat'.
'blat'+'ant'='BLATANT'
'that's' acts as a link.
(Other definitions for blatant that I've seen before include "Offensively obtrusive" , "Totally obvious" , "Very noticeable and obtrusive" , "Offensively obvious" , "Brazen, flagrant" .)