Reason North American lake must be blasted (8)
I believe the answer is:
infernal
'blasted' is the definition.
(thesaurus)
'reason north american lake' is the wordplay.
'reason' becomes 'infer' (inferring is a kind of reasoning).
'north american' becomes 'na'.
'lake' becomes 'l'.
'infer'+'na'+'l'='INFERNAL'
'must be' acts as a link.
(Other definitions for infernal that I've seen before include "Of hell, or tiresome like a nuisance" , "To do with hell, or informally detestable" , "Relating to the underworld" , "Blessed; damned" , "Of the nether regions" .)