Try to bind the snow mode hotkey and activate it in a safe place. What's probably happened is a critter has fallen into the river and gotten stuck. Snow mode will push them to the surface and will A) allow them to scurry off to disappear, or B) sprint towards you and do the scary thing before scurrying off to disappear.
That has been the most common cause of permanent meta paranoia for me, when it wasn't Krappus lurking after being purged by console.