Watershed follows start of broadcast link (6)
I believe the answer is:
bridge
'link' is the definition.
(both can mean to join or connect)
'watershed follows start of broadcast' is the wordplay.
'watershed' becomes 'ridge' (a watershed is a ridge of land in water).
'follows' means one lot of letters go next to another.
'start of' suggests taking the first letters.
The initial letter of 'broadcast' is 'b'.
'ridge' put after 'b' is 'BRIDGE'.
(Other definitions for bridge that I've seen before include "Card game - pontoon - couple" , "Span of popular card game" , "Game; crossing" , "Spanning structure to allow passage" , "Overpass" .)