Report of unsecured vessel in European lake (7)

I believe the answer is:

lucerne

I'm a little stuck... Click here to teach me more about this clue!

'lake' is the definition.
(Swiss lake)

I don't understand the remainder of the clue.

(Other definitions for lucerne that I've seen before include "Forage crop" , "Swiss canton, city and lake" , "Fodder crop - lake" , "Place beside lake" , "edible plant" .)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app