Island between river and a lake: closed area of Venice (6)
I believe the answer is:
rialto
'area of venice' is the definition.
(I've seen this before)
'island between river' is the wordplay.
'island' becomes 'alt' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'between' indicates putting letters inside.
'river' becomes 'rio' ('river' in Spanish).
'alt' going into 'rio' is 'RIALTO'.
'and a lake closed' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for rialto that I've seen before include "Area famous for 7 [ABRIDGE]" , "District in Venice and in south Dublin" , "Venice area with famous bridge" , "Venetian district" , "Old market" .)