Hour 4: X.E.23 -> X.H.24 (2' of rusted barbed wire)

The river flows directly west, but there's a fork in it that merges two smaller rivers: One from the north, and one from the south. Due to the size of the intersection - easily 50 feet wide and with fast currents - this diverts Senku's path back south again.

Hour 5: X.H.24 -> X.K.26 (bundle of watercress)
Hour 6: X.K.26 -> X.M.29 (heavily rusted bucket - there are quite a few corroded holes in the bottoms and sides)

At this point the north-south river bends east and plunges into the thicker parts of the jungle, significantly slowing Senku's progress even while following the banks of the river.

This upriver branch Senku is following is smaller than what he saw at the beach - roughly 30 feet wide, but muddier and a bit slower-moving. The sediment is slowly transitioning from sandy to dark and muddy the further upstream he travels. He sees plenty of vines growing on the trees here, but he doesn't spot any that look thick or sturdy enough to be used as ropes, or ones that could stand up to being threaded together.

Senku now has 2 hours left before Night 001.