unfortunately my answer is "i always knew".
in my understanding of being a deity, i'm not just a random spirit because of the level of knowledge and control i have over my element and all that interacted with it. i was a complete river--i had whole ecosystems within and around me that i knew how to care for, knew what it entailed, what the consequences of various issues and solutions would be, etc.
if i were a simply water spirit, i might have just been a pond, or a spirit made of a smaller amount of water. but the sheer size i was, and the amount of control over the forces of nature (including my ins with other types of spirits, in order to help those humans that asked my assistance) made me far more,,, advanced?