Which country has the most natural lakes?

Canada, with something like two million - more than the rest of the world combined, and roughly a fifth of all the fresh water on the planet's surface. Nine per cent of the country is covered by fresh water.

They are there because of ice. The Laurentide ice sheet sat on the whole region until around 10,000 years ago, gouging out basins as it advanced and leaving behind a chaotic landscape of scraped rock hollows and dammed valleys as it retreated - and the ground is still rising back up, having been pressed down by a kilometres-thick weight, at up to a centimetre a year in places around Hudson Bay.

Finland, Sweden and Russia have the same story for the same reason. Isostatic rebound is also slowly changing the map: land around Hudson Bay is emerging, shallow lakes are draining, and in Scandinavia harbours built in the Middle Ages are now inland. The Great Lakes hold about a fifth of the world's surface fresh water on their own, and are a single connected system draining through the St Lawrence - which is why an invasive species entering one of them tends to reach all of them.