Okay, so, Men communicate in sounds, and in the same way water will make certain sounds when moving in certain patterns (clunk if you drop a rock in, hiss if you force it through a narrow aperture under pressure, etc.), some shapes of mark represent sounds. This will not do the river Maia that much good since she's not familiar with the spoken language, but that's the underlying idea. Here are example written sentences all of which are themed around water/rivers/lakes/rain/waterfalls/snow/i
Maybe highlight the problems in red; the map is gorgeous but it's not necessarily obvious to Men which changes are problems and which are just changes. Other than that, seems great.
I have to breathe, so I'm not sure I can best appreciate the caverns without equipment I don't have, but I'm sure they're lovely.
And Loki flies back and says it seems to have been a benign river Maia and they can float messages in the river for her if they need something river-related but keep it down to once a year at most and she will respond with pictorial maps.
Oh, and do not mess with the river without permission, it's the Maia's and she wouldn't like it. Also you know how Elves are kinda... slow? Maiar are like that too and they might have to be patient. But she seems nice.
Loki gives an astronomy lecture, with the usual disclaimer that what she knows is planets in general and not this weird planet's weird astronomy; but she did see an eclipse or two on Midgard and it was like that.
Loki can attach illusion telescopes to sticks! They will not get you as far as Elf vision but they should help. Note: stars are less starlike than they appear.
She's starting to be a little deadline-conscious. Huan said five years. Could be longer; could just really be five. She apprises people of this deadline: she is not sure what will happen or when, but she does not want it to be a complete surprise.