Oku-Nikko Ramsar Wetlands was added to Your Favorites!
Nikko NP, Tochigi
Claim this place to tell your story your way.
Oku-Nikko’s Ramsar site brings together parts of Lake Yunoko, the Yukawa River, Senjogahara and Odashirogahara. Its 260.41 hectares were listed in 2005 under a criterion for representative or rare wetland types—not a huge bird count.
A meadow can briefly become a lake. After heavy rain, water gathers in low parts of Odashirogahara to form the temporary “Odashiro Lake,” a rare appearance Nikko City says happens every few years.
Senjogahara’s open marsh was once a lake more than 10 meters deep, formed when an eruption of Mt. Nantai dammed a river. Volcanic material, sediment and dead aquatic plants gradually filled it in.
Each autumn, kokanee salmon—called himemasu in Japan—swim from Lake Chuzenji into the Yukawa to spawn. The fish became part of local food culture, inspiring the saying that the lake’s autumn colors begin underwater.
In 1902, Scottish merchant Thomas Glover helped bring 25,000 brook-trout eggs from Colorado to the Yukawa. A typhoon wiped out the first batch, but a later release thrived, helping launch Japan’s fly-fishing tradition.
The name Senjogahara means “battlefield plain.” Local folklore says the gods of Mt. Nantai and Mt. Akagi took the forms of a giant serpent and centipede to fight over Lake Chuzenji; an archer helped Nantai’s side win.
Senjogahara contains all 3 major wetland types: raised bog, nutrient-rich fen and the intermediate type between them. One broad marsh is actually a patchwork of very different growing conditions.
Hot-spring seepage keeps a corner of Lake Yunoko open even when much of the lake freezes. That small patch of unfrozen water is a winter refuge for ducks such as mallards and Eurasian wigeons.
Latham’s snipe breeds in the wetlands of Senjogahara and Odashirogahara, then migrates to eastern Australia for winter. This long-distance traveler is one reason these highland marshes matter far beyond Japan.
Along the Yukawa, sedge roots bind soil into rounded hummocks called yachi-bozu—literally, “marsh bald heads.” Their roots help the mounds resist flowing water and erosion; in summer, leafy growth gives the “heads” a shaggy look.
A single white-barked birch stands out in Odashirogahara’s open grassland. Locals call it “the Lady,” and the tree has become a symbol of the area—and a favorite subject for photographers.
Around Odashirogahara, natural Japanese-larch woodland survives alongside planted trees. Such natural stands are rare in Japan, so this woodland is protected as an academic reference forest.
Deer fencing has helped a colony of native Japanese thistles, noazami, recover at Odashirogahara. The comeback is a visible reminder that protecting a wetland can sometimes mean keeping hungry visitors out.
For decades, volunteers and agencies have removed invasive North American Rudbeckia around Senjogahara and the Yukawa. It has nearly disappeared from the marsh, but persists elsewhere nearby, so the work continues.
Lake Yunoko’s water clarity once fell to 1.8 meters as sludge accumulated from wastewater and spring seepage. Carefully planned suction dredging began in 1992; by August 1994, measured clarity had improved to 3 meters.
