Why can't the Others go around the Wall at sea?

Question

As explained in a few earlier questions, the Wall does not extend all the way to the sea on the East, and the castle there is essentially undefended anyway. Thus, wildlings -- and Stannis' army -- were able to go around it undetected.

We know that the Others and the wights they raise can't cross through the Wall, and I think we can assume that it's built to stand up to any attacks they make trying to bring it down. But there does not appear to be any reason they can't just go around like anyone else.

Possibly related: in the TV Show, we actually see the attempted evacuation of Hardhome, and the Night King allows Jon Snow and his human army and civilians to flee back to their boats to safety, even after raising a massive army of wights. You could interpret this as merely a psychological ploy, but it may be a hint that the dead can't cross the water either.

Has there been any indication (books or show) that the Others/White Walkers and their army of wights are blocked by open water, or are somehow tied to the land of the Frozen North, or that there's any other obstacle keeping them from just sailing/swimming around the Wall?

Answer 1

Unknown

We essentially don't even know if they can or not. It could simply be the fact that they haven't, because, reasons.

One reason could be that they are biding their time to wait for a long winter, magic to return, or their forces to build up.

The other reason could be that they just don't know about the gap. They seem to have been "dormant" for millennia, and the Wall was built after their defeat. Who's to say that they have travelled as south and tested the defences?

The other thing we don't know much about is the magical ward placed on the Wall. Is it tied specifically to the physical structure of the Wall, or a general line from the eastern coast to the western coast. Like would an Other get stopped against dead space when they try to walk past the gap?

Let's consider logistics. Do the Others have boats? Can they walk on water? Does the water freeze as they near?

One thing's for sure, there are mentions of the dead being in water, on a few occasions on A Dance With Dragons (during Jon's chapters):

Dead things in the woods. Dead things in the water.

This makes me feel that the undead may not be so adverse to the water as we might think.

Answer 2

As of Game of Thrones Season 7 Episode 6, "Beyond the Wall", it would appear that the wights are not the best in water. I'm still not entirely convinced if they can swim or not (see: chains and grabbing Tormund's legs), however, they do fall into the water and seem to sink so it would point out that they aren't the best in water. See the following video (starts at 1:09 in case the link doesn't work).

The wights also then wait it out until they know that the lake has frozen over once again. This isn't conclusive proof that they can't swim because there could be a number of other reasons why they'd wait. For example, minimise losses, they're in a worse position coming out of the water, why attack when they have no chance of escape etc.

The evidence from this episode, along with Hardhome as mentioned in the OP, would seem to suggest that the wights at least can't swim.

The White Walkers are, however, a different thing altogether and it hasn't been shown one way or another if they can swim or even freeze water. They can do things with ice we wouldn't believe, see their swords and spears.

When the White Walkers attacked the cave of the Children of the Forest in Season 6 Episode 5, "The Door", the fire parts when the White Walkers get near. This isn't evidence that they could freeze water but does show that they bring the cold with them and so have some potential to freeze it.

For the books we have even less information but they are covered in @Möoz's answer.

Answer 3

The wights can cross the wall as shown by the two dead rangers that are brought back in the first book (Game of Thrones). One comes back to attack the Commander and causes the fire that burns Jon's hand.
The wight are semi-mindless attackers but they essentially can go anywhere in the world and are only stopped by fire. The Others including the king need the night and perhaps the cold as a source of power. They wait until the long night (winter) to cross the wall and become dominant south of the wall. The wall has magic that stops them but you are right in thinking they can just cross the water in boats which is probably what they do. This is just info from the books, I have not seen the most recent season of the TV show.