Disease disseminated by the ocean (7)
I believe the answer is:
seaside
'by the ocean' is the definition.
(I've seen this before)
'disease disseminated' is the wordplay.
'disseminated' indicates anagramming the letters.
'disease' with letters rearranged gives 'SEASIDE'.
(Other definitions for seaside that I've seen before include "Disease (anag) -- coast" , "holiday location" , "Old song 'I do like to be beside the . . . . . . .'" , "Holiday destination" , "Ocean shore" .)