Gondola, out of its depth, capsized in lake (6)
I believe the answer is:
lagoon
'lake' is the definition.
(lagoon is a kind of lake)
'gondola out of its depth capsized' is the wordplay.
'out of its' suggests deleting specific letters (the word lacking or 'out of' particular letters).
'depth' becomes 'd' (abbreviation in geometry).
'capsized' is an anagram indicator.
'gondola' with 'd' taken away is 'gonola'.
'gonola' anagrammed gives 'LAGOON'.
'in' is the link.
(Other definitions for lagoon that I've seen before include "Water cut off by coral reefs" , "A slat-water lake" , "Atoll's enclosed water" , "Atoll lake" , "... separating off this water?" .)