KUSHIRO, Hokkaido—“Marimo” moss balls, the fuzzy green spheres that have brought fame to Lake Akanko here, are shrinking because of global warming, a research group found. The maximum ...

Think about swimming in a lake or pool between 5-to-8 feet down; you can still see your feet but it’s starting to get hazy. That’s the same amount of light that touches the Marimo moss ball in ...