The first boy cringes at Faelar's question, but the second boy says, "Well, sir, I guess I don't rightly know. But the grown-ups all say to stay away from it and if you put a stick in it... well, the stick don't come back out!"
Penthar's detect evil reveals that there is indeed an evil presence in the area. Upon further observation, he finds that there is but one aura, and it is a strong one. After about 12 seconds of concentration, it is clear that the river is emanating the strong evil aura.
OOC: In case it isn't clear, each round of a detect spell yields more information so I have split it into three different sections. I assumed you held it for three rounds, but if you don't, then just don't read (or at the very least, pretend that you haven't read =P ) the other sections.