Icy city spies will infiltrate close to Poyang Lake (7)
I believe the answer is:
glacial
'icy' is the definition.
(I know that icy can be written as glacial)
'city spies will infiltrate close to poyang lake' is the wordplay.
'city' becomes 'LA' (Los Angeles).
'spies' becomes 'CIA' (Central Intelligence Agency).
'will infiltrate' is an insertion indicator.
'close to' indicates one should take the final letters (the close/ending of).
'lake' becomes 'L' (geographical abbreviation).
The final letter of 'poyang' is 'g'.
'la'+'cia'='lacia'
'g'+'l'='gl'
'lacia' put into 'gl' is 'GLACIAL'.
(Other definitions for glacial that I've seen before include "Cold and icy" , "Extremely cold" , "Frigid" , "Ice cold" , "Of slow moving ice masses" .)