Apparently certain rooms in the River Nanthor are coded such that you can walk on them without a boat or being able to fly. I landed with my arial, and then continued to walk on the river. Only a bit later did it say that I needed a boat.

<100%hp 100%m 11%mv 10750tnl> The river Nanthor
You float lazily on this peaceful river, eyeing the strange fish
swimming below. The river continues to run from the southwest to
the northeast here. On all other sides, the plains come up to meet
the water.


A minnow searches the water for tasty insects.

<100%hp 100%m 9%mv 10750tnl> l e
The river continues downstream to the northeast.

<100%hp 100%m 9%mv 10750tnl> e
The river Nanthor
You float lazily on this peaceful river, eyeing the scenery
around you. The river continues to run from the northwest,
turning a little to the south here. On all other sides, the plains
come up to meet the flowing water. Small fish of various bizarre
colors swim in and out of underwater vegetation and miniscule air
bubbles rise up from the mud on the bottom.



<100%hp 100%m 6%mv 10750tnl> af

You feel the currents drag you along.
The river Nanthor
You float lazily on this peaceful river, eyeing the strange fish
swimming below. The river continues to the east and bends slightly
to the southwest. Due west and north you see the plains running
right up to the river's edge.


A minnow searches the water for tasty insects.
A minnow searches the water for tasty insects.

<100%hp 100%m 5%mv 10750tnl> You are affected by:
Spell: 'armor' modifies armor class by -20 for 4 hours.
Spell: 'invis' for 5 hours.
Spell: 'infravision' for 16 hours.

<100%hp 100%m 5%mv 10750tnl> e
The river Nanthor
You float lazily on this peaceful river, eyeing the strange fish
swimming below. The river continues to the west and south. To the
north you see the mountains and to the east a dark forest leads right
up to the river's edge.



<100%hp 100%m 9%mv 10750tnl>
You need a boat to go there.