Kinda like the slime in the sewers. [about what he's going to compare it to, since marinas are not places he's been to in his life. none he recalls at least. shouto's explanation works well enough, though he's not about to go touching the damn thing.

touya reaches out with a leg and props the sole of his foot on the rim of the boat's side, then gives it a slight push to rock it atop the shore and the water, sending a few ripples out into the water.]

If the boat's not been here long, then it means someone was here recently. [unless it's been drifting for a while, and just now got stuck in this part of the river. so far nothing's jumped out of the water or made any other movement, so he's deeming the river relatively safe... for now. not going in it though.] They are. Met two other people explorin earlier. One yesterday and one the day before.

[they made sure to leave marks or signs that they went one way or the other.]

If someone's already been down a tunnel, then they either already found what might've been in there, or died in the process.

[so an argument for going down a previously-explored tunnel, with the pros being traps already sprung, but the cons being, provided the explorers survived the dangers, anything of worth already being gone.

oh and finding dead people.]