Wise to be navigating initially in lake? (5)
I believe the answer is:
ernie
'wise' is the definition.
(Ernie Wise)
'navigating initially in lake?' is the wordplay.
'initially' indicates taking the first letters.
'in' indicates putting letters inside.
'lake?' becomes 'erie' (Lake Erie is one of the Canadian/US 'Great Lakes').
The first letter of 'navigating' is 'n'.
'n' going inside 'erie' is 'ERNIE'.
'to be' is the link.
(Other definitions for ernie that I've seen before include "Premium Bond selecting machine" , "Computer selecting Premium Bond winners" , "___ Wise, d. 1999" , "Bondsman" , "Man - chooses Premium Bond winners" .)