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I am writing a speculative fictional story set in the future, where the bacteria Vibrio vulnificus mutates and makes life so dangerous for humans along the coast that everyone has to retreat into the center of the North American continent (actually around the great lakes in Michigan and Canada). I don't even know if this is actually possible. I suppose a bacteria could mutate into anything, theoretically, but I want to have a general idea of how it would actually contaminate all clean water sources in the bottom half of the united states.. or at least 500 miles inland on both coasts. Any creative ideas? Possibly it would affect the rain that falls in certain places?

I wanted to have the sea levels rising also that would push them further inland, but the sea levels rising that much seem physically impossible (ie even if all the ice melted they wouldn’t rise 100m).

I’m just looking for a slightly deeper explanation than “the bacteria mutates and spreads”- currently this bacteria only kills people if they eat it, but I’m wondering if it could kill people by getting in the water supply or the rain.

"Vibrio vulnificus is a bacterium that normally lives in warm seawater and is part of a group of vibrios that are called "halophilic" because they require salt. How do persons get infected with Vibrio vulnificus? People can get infected with Vibrio vulnificus when they eat raw shellfish, particularly oysters."

One problem is that if it remains halophilic then it wouldn’t contaminate drinking water. Maybe it mutates to freshwater and starts contaminating all the lakes and fresh water rivers, but humanity finds a way to dam up the great lakes and keep them uncontaminated. For now… dun dun dun.. then that’s where the story picks up.

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    $\begingroup$ Are you limited to the exact source of threat (bacteria), or it could be something else? I am in doubt that any bacteria could contaminate that much surface (daytime! UV! And bacteria would run out of food) for people to be forced away from shores. $\endgroup$
    – Vesper
    Commented Apr 4 at 14:38
  • $\begingroup$ Not really. I was looking for a reason for humanity to shrink and center around the great lakes and I thought of this toxic ocean bacteria. Open to other ideas! $\endgroup$
    – Rachel Cox
    Commented Apr 4 at 20:19
  • $\begingroup$ "Maybe it mutates to freshwater": you're basically describing V. cholerae at this point. That's something we already have to control and keep out of drinking water. $\endgroup$ Commented Apr 5 at 5:16
  • $\begingroup$ Cholera, Tyhpus etc. There's plenty of nasty stuff that gets into fresh water without worrying about salt water bacteria, your problem is that nothing like this would actually affect our ability to live by the sea as that's not where our drinking water comes from and there's minimal risk of airbourne contamination from water based toxins. $\endgroup$
    – Separatrix
    Commented Apr 5 at 8:06

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The drinking water cleaning process is (or at least can be) very aggressive. There's little scope for stuff surviving in there that's not wanted, especially in places where sunlight is plentiful. I think whatever effect you're looking for, it has to be effective without needing to contaminate drinking water.

It sounds like you need a two-pronged attack. I suggest both prongs be harmful algal blooms, albeit of different types.

New strains of toxic marine algae can form deadly "red tides". By themselves these aren't enough to drive people inland, though once all the fish are dead and the tourists have either fled or joined the fish, there's a lot less incentive to stay there. Combine that with sea level rise and an increase in serious coastal storms (thanks, climate change!) and you can destroy coastal cities and generate exciting aerosols of neurotoxic algae that can blow inland a few miles and kill things living a little away from the coast, too. Sure, people might return when the weather is nice, but no-one is gonna spend that long in areas where bad weather brings vomiting, brain damage and paralysis.

This can be combined with new forms of cyanobacteria that like freshwater. There's a general increase in the stuff all over the world, again thanks to warming climates. Whilst it might not be practical to have drinking water contaminated, agricultural water supplies are not treated quite so aggressively and so livestock may be at risk and food crops could be contaminated with bacterial toxins. You could still live and even farm in such an area, but it'll become harder and more expensive and the range and yield of things you can produce will go down. A general northward exodus would make life less appealing and more difficult for those who try to remain, as infrastructure maintenance drops and things like medical care become harder to come by.

Unfortunately, the Great Lakes are already the site of toxic algal blooms, notably Lake Erie. I'm not sure quite how you'd reconcile this with your setting, unless the new strains of cyanobacteria like the warm, and the mutations of interest make them more cold tolerant which combined with climate changes mean the great lakes become more hospitable to them.

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  • $\begingroup$ Great answer. Thank you! One idea is that there is a concurrent societal breakdown that destroys the water purification infrastructure so that incites an emergency retreat to Lake Superior, the cleanest and safest lake. Perhaps once there, the remaining humans are able to keep that water safe, at least temporarily. $\endgroup$
    – Rachel Cox
    Commented Apr 4 at 14:51
  • $\begingroup$ @RachelCox, the Great Lakes, particularly along the coastlines, are contaminated with all sorts of exciting chemicals. It takes far more purification technology to remove chemical contamination than it takes to remove bacterial contamination. $\endgroup$
    – Mark
    Commented Apr 4 at 22:51
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The important factor is physical transport of the bacteria. The only way to transport long distance over land going from the sea inland is by air. The bacteria need to be able to go up on the beach, dry out enough to be picked up by wind, and be blown hundreds of miles inland. A steady wind of 25 miles per hour blowing for 20 hours will move 500 miles inland. (That is how moisture from the Gulf of Mexico gets up into the plains states to produce the monster storms.)

An alternative means is to catch a ride on migrating fish. Salmon and steelhead trout will migrate from the ocean hundreds of miles upriver when there are not dams in the way. This will limit the spread to rivers, lakes, and streams.

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  • $\begingroup$ I was thinking the Mississippi would be contaminated.. thus blocking the humans from going westward. The humans trapped west of the Mississippi might die from lack of fresh water. $\endgroup$
    – Rachel Cox
    Commented Apr 4 at 14:52
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    $\begingroup$ @RachelCox Humans can cross contaminated water simply by hollowing out a log. A white oak log won't let any water in. There are plenty of rain water filled lakes out on the prairie. Water that goes down into the water table and comes out in a spring is very clean. $\endgroup$
    – David R
    Commented Apr 4 at 18:37
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I'm struggling to find any data on water temperatures, so this would need to be an area of research, but according to this paper, shows a pretty strong sensitivity to temperature. That being the case, and assuming the temperatures of the Great Lakes will support (I think it does based on this paper and current data), then overcoming its aversion to fresh water could be a great way to drive people inland, including to gathering around the Great Lakes. These effects would be seasonal and highly responsive to increasing global temperatures, meaning it could, in fact, give the story a tciking clock!

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    $\begingroup$ Do you mean that in the story, the bacteria mutates and starts spreading into the cooler and fresh water? I know right now it's only in warm salt water, in the story it would have to mutate somehow. $\endgroup$
    – Rachel Cox
    Commented Apr 4 at 15:50
  • $\begingroup$ @RachelCox My thought was that it only mutates to handle fresh water. The response to temperature we see in the bacteria already; its growth is severely limited below around 8.5C (47.3F), and even below 13C (55F), it's pretty inhibited. That being the case, since most fresh water flows from higher elevation to lower, temperatures in rivers is often caused in large part by snowmelt from those higher elevations. So, basically, the further away from the mouth, the cooler the water. $\endgroup$
    – Amocito
    Commented Apr 4 at 16:29

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