Strange how millrace ends in the lake (5)
I believe the answer is:
eerie
'strange' is the definition.
(eerie means odd or strange)
'millrace ends in the lake' is the wordplay.
'ends' indicates one should take the final letters.
'in the' indicates putting letters inside.
'lake' becomes 'erie' (Lake Erie is one of the Canadian/US 'Great Lakes').
The final letter of 'millrace' is 'e'.
'e' put into 'erie' is 'EERIE'.
'how' acts as a link.
(Other definitions for eerie that I've seen before include "Spooky, macabre" , "Uncannily strange" , "Mysterious" , "Unnerving" , "Frighteningly odd" .)