The German disappeared in an English river (7)
I believe the answer is:
derwent
'an english river' is the definition.
(I've seen this before)
'the german disappeared' is the wordplay.
'the german' becomes 'der' ('the' in German).
'disappeared' becomes 'went' (I've seen this before).
'der'+'went'='DERWENT'
'in' is the link.
(Other definitions for derwent that I've seen before include "Derbyshire or Yorkshire river" , "River; lake, --water" , "N. Yorks river" , "English runner" , "N. Yorkshire river" .)