Fortunately, Link has a lot of Brightbloom seeds. Whenever they move from one area of light into darkness, he pulls out another one and tosses it ahead.

He also frequently stops to pick up any mushrooms he sees. Or lizards. Or frogs. Really, practically anything and everything. All of these are whisked away into the small pack at his belt, which really isn't big enough to fit all of these.

At the water, he shrugs. "Could be an underwater river." He's seen those before, back in Hyrule. There were a few he knew of that twisted through underground spaces, before eventually reaching the sea. It happened.