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Oze NP, Fukushima / Gunma / Niigata
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Some Ozegahara islands are peat mats torn from a pond’s edge or lifted from its floor. Before boardwalks, people climbed aboard and drifted around; others only look free-floating, staying rooted below.
Smooth, comma-shaped ponds are thought to be old river bends cut off as oxbow lakes. Irregular ponds likely began in wet hollows called shurenke, where peat built up more slowly than on surrounding hummocks.
At Ryugu, a stream vanishes into the marsh and reappears across the boardwalk. A hut keeper who saw it imagined the hole led to the Dragon Palace—and the place kept the name.
Researchers studying Ryugu’s underground structure infer that a landslide around the 7th century buried a river channel, helping explain the hidden flow beneath this part of Ozegahara.
Oze-kohone was discovered and named in Ozegahara, but it also grows on Mt. Gassan in Yamagata. Its flower’s red stigma is a handy clue for recognizing this distinctive pond plant.
A 2017 survey of 40 Upper Ozegahara ponds confirmed two opposite trends since the 1970s: sheep’s water-lily has spread, while Oze yellow pond-lily has declined.
Ozegahara’s ponds are not static: a 2017–19 survey found 80 fewer than on the 1998 list, mainly shallow ponds dried in dry years. Another study estimated 4 pond edges advanced about 1.5 cm a year.
After a 2019 flood, researchers found fewer shoreline invertebrates in more flood-affected ponds, especially midge larvae. Floodwater may have washed them out and brought fish predators into the pools.
