Take a minute and imagine the wooly mammoth from an animated movie franchise that may or may not also feature a slow-moving, fast-talking ground sloth and a sabre-toothed squirrel that is obsessed with collecting acorns.

Got that mammoth in your head?

Now, imagine that mammoth on a small island (roughly the size of Walt Disney World) off the Alaskan coast.

The mammoth is part of a small heard of mammoths that live on this island. They don’t know it, but they are the last mammoths alive. They are alive at a time when humans have learned to smelt copper and lead, make wheels, and train silkworms to produce enough silk that people can actually use.

Humans have likely hunted mammoths in some parts of the world to extinction. Hunting activities are likely to have added yet another environmental pressure to mammoths, which were likely already experiencing population decreases as the world shifted from the Last Glacial Maximum to the warmer Holocene Epoch.

Those mammoths are slowly going extinct.

Discover magazine wrote about the collapse of the mammoth population in October 2013—and hinted then at what might have killed the last mammoths on St. Paul Island. Sea-level rise. Perhaps they had an inkling of how close to right they were.

New research from Pennsylvania State University suggests that these mammoths didn’t die because hunters came by boat and killed them off, which was one of the previous theories (there is no evidence that humans were ever on the island before the late 1700s). Instead, they probably died of thirst.

St. Paul Island didn’t have rivers or springs—the only fresh water came from shallow lakes. As sea levels rose, these shallow lakes underwent saltwater intrusion (between 7,850 and 5,600 years ago). In short, as the climate became drier, and as large sheets of ice that had been present during the ice age melted and caused sea-level rise, the lakes on St. Paul became smaller, shallower, and saltier.

Part of what’s heart-breaking about the tale of these last mammoths is that, in all likelihood, they made things worse for themselves. As the number of lakes with drinkable water dwindled, the mammoths would have been forced to visit a decreasing number of fresh water sources. Their repeated movement to and from these select lakes would have had a significant negative impact on the shoreline vegetation, which would have eroded the banks, and eventually led to sediment deposits that filled in the lakes.

Lack of access to fresh water is seen as a likely model for extinction in the future—and it’s important to note that mammoths are not the only animal to have gone extinct this way, and that we have a recent example. The Bramble Cay melomys (Melomys rubicola), a small island rat that is endemic to a single island in the middle of the Great Barrier Reef is believed to have gone extinct, at some point in the past seven years, because of saltwater intrusion.

So why should we care about what likely happened to the mammoth or the melomys?

Most basically, because in some places drinking water is at stake—even if the sea-level rise is just temporary, because of a storm event. (It’s important to note that some sea-level rise as a result of storms is permanent. The coast of Louisiana, for instance, lost a lot of coastal wetlands after Hurricane Katrina.) Beyond that, sea-level rise also impacts our infrastructure and economies.

We can slow down impacts related to sea-level rise by not acting like the mammoths—which means making sure that we protect shorelines. This might come in a variety of forms, ranging from designating state parks or national shorelines to coastal management options, which might include hard engineering techniques (think sea walls or tidal barriers; these have fallen out of favor because they interrupt sediment transport) or soft engineering plans (including marshland creation and sand dune creation). In some places, these management techniques can help protect coastal areas from general sea-level rise or storm surges—and can also help protect drinking water from saltwater intrusion.

One technique that’s being used in coastal areas to stave off saltwater intrusion is the use of injection wells. Injection wells allow potable water to be pumped into aquifer containing fresh groundwater. This increases the pressure of the fresh water, which keeps saltwater from (further) intruding. Read more about saltwater intrusion in our latest blog, here.

Other areas, however, are trickier. There are islands in the South Pacific where people are having trouble getting enough fresh water, and low-lying lands elsewhere are at risk too. Russell Graham, of Penn State University, who led the research on the mammoth extinction warns that people in Florida are “waiting for big waves to come in and flood the state, but really the salt water is coming in from below their feet. It will really limit the availability of fresh water.”

For most of us, this type of change is hard to imagine—aquifers were something we learned about in school but might or might not be able to actually conceptualize, and besides, isn’t SLR going to look like that half hour scene from A.I. Artificial Intelligence (2001) where Haley Joel Osment sits at the bottom of the ocean near flooded Manhattan waiting for the blue fairy?

If you’re having trouble imagining what saltwater intrusion looks like—and what it means for fresh water sources—check out this cool experiment (and maybe also try it with some children you know).

And in the meantime, enjoy your next glass of water.