A River Running

Once I was by a willow,
sitting by my favorite tree,
when out of the blue,
and it scared me too,
the river started running from me.
I asked it why,
But I could not see,
for away its mouth had run,
I dove in,
and strove to search,
to whence the river would come.
for two nights we swam together,
And on the third I found the sea.
and to this day,  I still don't know.
Why the river ran from me...