Tree and lake overlooking curved structure (5)
I believe the answer is:
larch
'tree' is the definition.
(larch tree is a kind of tree)
'lake overlooking curved structure' is the wordplay.
'lake' becomes 'l'.
'overlooking' says to put letters next to each other (down clues only).
'curved structure' becomes 'arch' (I've seen this before).
'l'+'arch'='LARCH'
'and' acts as a link.
(Other definitions for larch that I've seen before include "Coniferous tree with deciduous bright green needles" , "Supplier of timber" , "wood" , "Deciduous conifer" .)