Kanaalmunten
Despite the name, Kanaalmunten (literally, “canal coins”) can come from any recognized body of water: canals, rivers, ponds, bays, streams, oceans… even an abandoned swimming pool, if the conditions are right. Said conditions are: somebody has to accidentally lose a metal coin in the water, and the coin has to remain there undisturbed for at least a year and a day. When that happens, the coin becomes a Kanaalmunten.
Kanaalmunten are mostly useful as magical identification devices: they ‘glow’ when held by a magic-user or supernatural creature. This glow can only be seen by those who are themselves magic-users, or supernatural creatures, so it’s a good way to establish the esoteric bona fides of someone. Note that Kanaalmunten will not reveal the power level of a supernatural entity, nor will it do anything to determine whether or not that entity is honorable or truthful — but it does reveal poseurs and imposters, which is useful in its own right.
Also: Kanaalmunten are apparently inherently valuable to any sort of water spirit or entity. They trade them among themselves, and readily accept them as rewards. The older the Kanaalmunten, the more valuable it is to them — but even a new-’minted’ Kanaalmunten will be worth the esoteric equivalent of a bound stack of fifty dollar bills. This may not sound like much, but to give just one example: river gods rarely have bank accounts, and little use for paper money. Kanaalmunten makes it much easier to hire them for ‘small’ jobs, for a given definition of ‘small.’
Do water spirits mind when people dig in their domains for kanaalmunten? Also, if somebody dumps a body in a river with coins in the pocket and it stays there for a year and a day, are those coins kanaal munten?
1). If they get their cut? Nope. Not every area has a water spirit, though.
2). Yup.