Strangely frightening eastern lake (5)
I believe the answer is:
eerie
'strangely frightening' is the definition.
(I've seen this before)
'eastern lake' is the wordplay.
'eastern' becomes 'e'.
'lake' becomes 'erie' (Lake Erie is one of the Canadian/US 'Great Lakes').
'e'+'erie'='EERIE'
(Other definitions for eerie that I've seen before include "Scary, weird" , "Weird and disturbing" , "Spooky, creepy" , "Sinister" , "Weird, uncanny" .)