@KazemitsuSo like a sea god? Or like a water dragon god?
@DezuelHi, thanks for the interest! As for your question, yes but it is by no means easy. Gods are powerful entities who basically exist to uphold an aspect of creation. By killing a god you're basically killing the aspect that they uphold and leaving what remains of said aspect, broken. It'll still work but it won't be upheld to the fullest.
For example, lets say The God of War and the God of Peace got into a battle. The God of War overwhelms Peace, and kills him. Peace gets sent to place that not even the Gods know and War is the victor. Ever since Peace died, the Human's world has been at war on and off with only small time periods of relative peace. It doesn't have to be a full scale war to suffice either, even a small border skirmish counts.
Hopefully that helps!