Water searches are *really* hard. The water levels may have changed. There were three bodies of water to consider in the vicinity of the party. And if LE had searched the water for days and neglected to follow up on abduction theories, had she actually turned out to have been abducted, folks would have been coming for their heads then too, so they had to broaden their search.
...
It seems a little tacky to me that people are saying that LE discouraged them from searching Prosser—if they wanted to discourage them, they could have simply prevented it, saying it was an active investigation. LE did not do that.