Speak with water
Water, or the spirit that dwells within it, can speak to casters of the speak with water spell. It will know such things as what creatures drank from it last and what they looked like, where a particular fish is, or if a specific item lies at the bottom. It has no concept of names or time, and generally only remembers events that have occurred in the past week.
Note: This spell originally appeared in this form in the Earth, Air, Fire & Water supplement for the AD&D game from TSR. Their use here is for the purposes of providing context for the campaign only.