Old mines leave behind a a pressing problem: Huge holes that make the landscape look like a chunk of swiss cheese. But in Germany, some scientists and city planners are turning these into lakes.

The largest one will be the biggest artificial lake in Germany when it's done, with a shoreline of 26 kilometers or about 16 miles all around.

But it's not as easy as simply filling the holes with water. It takes a LOT of research to get this science right.

Interested in more environmental stories? Email us at [email protected]. We'd love to hear from you!

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