Article on excited UK Green insiders' legendary response to rising water level (6)
I believe the answer is:
eureka
'legendary response to rising water level' is the definition.
(Archimedes shouted 'Eureka' in his bath)
'article on excited uk green insiders'' is the wordplay.
I cannot really see how this works, but
'article' could be 'a' (the indefinite article in English) and 'a' is present in the answer.
'on' could be 're' ('on' can be mean 'with reference to') and 're' is present in the answer.
'uk' is present in the answer.
A single letter 'e' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for eureka that I've seen before include "Discovery announcement" , "discovery that's brilliant" , "Exclamation of triumph" , "Shriek of discovery" , "county seat in 23 [CALIFORNIA]" .)