One way lake gets covered by the plant (7)
I believe the answer is:
thistle
'plant' is the definition.
(thistle is a kind of plant)
'one way lake gets covered by the' is the wordplay.
'one' becomes 'i' (Roman numeral).
'way' becomes 'st'.
'lake' becomes 'l'.
'gets covered by' indicates putting letters inside.
'i'+'st'+'l'='istl'
'istl' placed within 'the' is 'THISTLE'.
(Other definitions for thistle that I've seen before include "Prickly weed" , "Scotland's emblem" , "Scots plant emblem" , "The Scottish weed?" , "Lithest sort of spiky plant" .)