Disinfect shore around lake (6)
I believe the answer is:
bleach
'disinfect' is the definition.
(I've seen this before)
'shore around lake' is the wordplay.
'shore' becomes 'beach' (I've seen this in another clue).
'around' indicates putting letters inside.
'lake' becomes 'L' (geographical abbreviation).
'beach' enclosing 'l' is 'BLEACH'.
(Other definitions for bleach that I've seen before include "Sterilising whitener" , "Whiten with a belch" , "Chemical whitener" , "Make colourless" , "Whiten - disinfectant" .)