It's a fantasy role-playing game.

DM: You are Grog Strongjaw, a goliath barbarian . You are the member of the famous group of adventurers. Previously,  The group of adventurers, Vox Machina, had found themselves in the Feywild, intent on discovering another one of the Vestiges of the Divergence, one of the many artifacts that they hope will aid them in their struggle against Thordak the Cinder King and the rest of the Chroma Conclave. They've defeated two of the members, three still remain, Thordak being the seeming powerhouse head of that troupe.
DM: So as you guys begin to prepare your attempt to cross the river, Keyleth concentrates. The river stalls for a moment, and then pushes past, seemingly unaffected. Mind you, the spell does seem to have an effect when you're having a better time concentrating, but it is a magical force versus a magical force, and you can see it actually angrily swells against the resistance. That's where the actual tension comes from. There is something living, like an entity that these rivers seem to almost mingle as.
Player: Are there a bunch of trees?
DM: There are a few sporadic trees scattered around, yes.
Player: How tall are they?
DM: They're not that tall. Some are maybe 15, 20 feet up. These trees specifically are a little more marsh-based. They're not quite swamp-based trees, but that's as tall as they get.
Player: And the river's 20 feet wide, right?
DM: No, these are maybe five feet wide.
