Run two sons across lake (6)
I believe the answer is:
series
'run' is the definition.
(both can mean a sequence of things)
'two sons across lake' is the wordplay.
'two sons' can mean two substitutions for 'sons'.
'sons' becomes 's'.
'sons' becomes 's'.
'across' is an insertion indicator.
'lake' becomes 'erie' (Lake Erie is one of the Canadian/US 'Great Lakes').
's'+'s'='ss'
'ss' placed around 'erie' is 'SERIES'.
(Other definitions for series that I've seen before include "Set of TV programmes" , "procession" , "Group of related radio/TV programmes" , "Similar things happening one after another" , "Sets in sequence" .)