Extreme Fishing ...

In comments on my review of Mt. Takao as a zombie survival spot, commenter’s Claytonian and Paul raised the complex and controversial issue of Zombies and water. Claytonian even went so far as to raise the radical (but in my opinion very interesting and challenging) notion that zombies might retain some human instincts:

come to think of it babies can swim so zombies might have the instinct left

This raises a lot of issues for zombipocalypse survival planning, since there are a lot of benefits to establishing a water barrier. In this post I’ll describe these benefits (essentially rehashing my response in comments) and then look at some of the possible planning problems that arise from consideration of zombies and water barriers.

The benefit of water barriers

Water barriers aren’t just good because of their ability to keep out zombies. If the barrier has freshwater, it provides a potentially unlimited source of water and sewage for a small community (only the latter if its seawater). Water barriers offer an uninterrupted view which, while it may be useless against zombies on the sea floor, is very useful for identifying incoming human threats – and these are not to be discounted in the post zombie world. If the water is flowing, it offers the potential for long-term construction of energy systems (water wheels). But perhaps most importantly, a water barrier contains fish, which means that in addition to establishing a buffer zone, a community on an island can use this water barrier as a source of (potentially unlimited) protein, which can be obtained with limited skills and without needing to make a great deal of noise or effort. Furthermore, it’s fairly likely that fish don’t attract zombies, whereas mammals might, so as a protein source fish are a much much safer option than farming. By finding a suitable island within a reasonable distance of a city, it may be possible to establish a sustainable community, with easy access to valuable resources in the city, that is relatively well protected from zombie assault. The biggest problem the survivors are likely to face is then going to be marauding groups of survivors: islands will be in high demand after the zombiepocalypse, and people will kill to take them.

Can zombies swim?

Water barriers will be most successful if zombies can’t swim, but the definitive text (World War Z, 2006) suggests that they can walk underwater, and that they will slowly spread out under the sea as they seek human prey. This means that eventually zombies will arrive at your island, and that in the science of that textbook, they will appear randomly and intermittently without warning. This means at the very least you will need to keep a constant watch, though a random process of diffusion suggests that the further your island is from shore the lower the rate at which zombies will arrive. Obviously some system of inshore nets or wires may help in the watch process, but these may require a lot of work and be hazardous to establish. Claytonian’s swimming suggests that Zombies will have a more purposive process of attacking islands, choosing to swim towards them if they sense food but otherwise not swimming – if one assumes that zombies function according to some kind of basic laws of energy conservation, they will presumably prefer the least energy inefficient method of movement when there is no reason to use a more intensive one. Of course, it may be that zombies aren’t governed by such constraints, and that hordes or individuals will occasionally choose to swim and can potentially swim huge distances without effort. This problem can still probably be partially managed on an island, since if it is more than a few hours from shore the action of wind and water will likely disperse hordes sufficiently to render them much less threatening if they stumble on an island.

So then, an important question arises: can zombies communicate and form hordes underwater, and do they retain the ability to hone on prey when travelling by water?

Zombie hording patterns

It seems reasonable to suppose that zombies find movement underwater more difficult than on land -there are special obstacles and the water impedes movement, not to mention the issue of currents – and that they require some kind of sensory function to identify prey. This suggests that even if a horde encounters evidence of humans living in an island within sensory distance of shore (e.g., light on an island 300m out) they won’t necessarily be able to approach it as a horde. Seeing the light, they enter water as a horde but once underwater they are disoriented, blind, no longer able to see the light, and the horde begins to break apart. Walking along the bottom they will soon enter lightless zones, and won’t be able to communicate; presumably then the horde begins to disperse, but furthermore, in those zones they will have no knowledge of where their target is. This suggests that the horde will then behave as a random entity, with zombies heading in all directions. Assuming they entered on a straight line path to the island, some will likely wash up ashore, but their arrival must surely be staggered and incoherent. The only way they can arrive en masse is if they are both attuned to each other through a supernatural force, and attuned to supernatural emissions from quite distant life forms. But there is no evidence from any of the extensive research on zombies that this is the case: they seem to require some sign that a human is there, and can even be fooled by smell (The Walking Dead, 2011) or by convincing acting (Shaun of the Dead, 2oo4) or by various forms of stealth and silence (28 Days Later, 2002).

This suggests that even if they can walk underwater and cross very large distances under the sea, zombies will not be able to attack an island as a horde with the same ferocity as they can attack a survival spot on land. In remoter areas this may mean it may be possible to run lights and sound at night, with relatively little fear of intrusion, even on an island relatively close (say, 500m) to shore, because even a large horde will be broken up by water and arrive in a staggered and easily destroyed fashion.


The obvious benefits of islands as a long-term sustainable community setting, combined with the potential for a water barrier to disrupt zombie horde accretion even when located quite close to land, suggests that islands are ideal survival settings regardless of the particular level of aquatic adaptability of the undead, and that even islands quite close to land – within sight of occupied areas – may be suitable survival settings in a zombiepocalypse. Of course, this doesn’t mean that you will be safe on an island 30m from the shore in Tokyo bay, but it does mean that a reasonably well placed island with no direct land access provides a very strong base to establish a community of survivors in relative safety. The value of islands as a survival location increases significantly if the survivors are fleeing in an area of very dense population (e.g. Tokyo or New York) since even if ultimately the island is overrun, its facility in slowing down hordes will provide survivors a location to regroup and gather supplies before moving on to a more distant island.

The most significant problem in choosing an island to escape to is likely to be human survivors, who will defend their location ferociously precisely because of these benefits. The best advice is to get there first, and heavily armed.