Italy’s sparkling water maintaining its river crustaceans’ order (7)

'order' is the definition.
(Isopoda is an example)

'italy's sparkling water maintaining its river crustaceans'' is the wordplay.
I cannot really see how this works, but
'italy's' could be 'is' and 'is' is present in the answer.
'water' could be 'po' (Po is an example) and 'po' is present in the answer.
The remaining letters 'oda' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?