Small lake surrounds university enclosure (5)
I believe the answer is:
pound
'enclosure' is the definition.
(I know that Pound is a animal pound)
'small lake surrounds university' is the wordplay.
'small lake' becomes 'pond' (I've seen this before).
'surrounds' indicates putting letters inside.
'university' becomes 'U' (abbreviation as in UMass).
'pond' enclosing 'u' is 'POUND'.
(Other definitions for pound that I've seen before include "Cars towed to it; hit heavily" , "Beat - poet, d. 1972" , "100 6 [PENNIES]" , "Caged poet" , "UK currency; weight" .)