You shouldn’t have weed in lake (5)
I believe the answer is:
tahoe
'lake' is the definition.
(Lake Tahoe in the USA)
'you shouldn't have weed' is the wordplay.
'you shouldn't have' becomes 'ta' (both can mean 'thank you').
'weed' becomes 'hoe' (I've seen this before).
'ta'+'hoe'='TAHOE'
'in' acts as a link.
(Other definitions for tahoe that I've seen before include "Lake/desert resort on the California-Nevada border" , "Lake in Sierra Nevada mountains" , "Nevada/California lake" , "US lake" , "Mountain lake" .)