It's creepy when first character goes missing in large lake (4)
I believe the answer is:
erie
'large lake' is the definition.
(one of the Great Lakes)
'it's creepy when first character goes missing in' is the wordplay.
'it's' becomes 'e's' ('e' can mean 'electronic' which is similar to 'IT').
'creepy' becomes 'eerie' (eerie can mean strange or creepy).
'when first character' becomes 'w' (1st letter of 'when').
'goes' becomes 'wees' (go can mean to urinate).
'missing in' suggests deleting specific letters.
'es'+'eerie'+'w'='eseeriew'
'eseeriew' with 'wees' taken out is 'ERIE'.
(Other definitions for erie that I've seen before include "Lake between Canada and the US" , "Buffalo's lake" , "Great lake in Eire" , "North american lake sounds spooky" , "One of the Great Lakes" .)