60 pieces · NaturePhoto by Jarrett Kow on Unsplash (Unsplash License). The Shirogane Blue Pond near Biei in central Hokkaido, Japan — bare larch trunks standing in flat turquoise water that holds their reflections, a bank of rust and coral autumn foliage along the far shore, and the snow-streaked peaks of the Tokachi range on the horizon.
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The Blue Pond at Biei, Hokkaido
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The Blue Pond at Biei, Hokkaido
This is the Shirogane Blue Pond, which sits in the hills above the farming town of Biei in central Hokkaido, on the Biei River below the Tokachi volcanic range. It is one of the more unlikely beauty spots in Japan, because nobody set out to make it. After Mount Tokachi erupted in the late 1980s, engineers built a series of erosion-control barriers along the river to catch any volcanic mudflow before it reached the town downstream. Water backed up behind one of those concrete works and spread into a shallow basin of standing forest. The larch and birch there drowned where they stood, and their bare grey trunks — the ones rising out of the water across the whole lower half of this frame — are what is left of the woodland that was there before the barrier went in.
The colour is a chemical accident of the same landscape. Spring water from the Shirahige Falls, a short way upstream, carries dissolved aluminium down into the Biei River; where the two meet, the aluminium forms extremely fine particles that stay suspended rather than settling out. Those particles scatter the shorter, bluer wavelengths of sunlight back toward the surface, so the pond reads as milky turquoise instead of clear. It is not a fixed shade. Light, weather, and how much silt the river is carrying all shift it, so the water can look pale and opaque one day and a deep cobalt the next, and a grey sky flattens it out entirely. In this photograph it is at its best — a saturated blue-green under a clear autumn sky, holding every trunk as a long vertical reflection.
That gives the puzzle three very different regions to work through. The thicket of bare trunks is the obvious place to start: hard dark lines against flat colour, every piece with an unambiguous edge to match, and the reflections below the waterline repeating the same shapes upside down. Next take the band of autumn foliage along the far shore — sort those pieces by hue rather than by shape, because the colour runs in a readable sequence from deep red through coral and rust into ochre and brown near the ground. Save the open water and the sky for last. The water is not uniform, so look for the faint horizontal bands of lighter and darker turquoise and build along them; the sky is the hardest part of the picture, with only the thin wisps of cloud and the snow-streaked ridge on the horizon to give you a fix.
How to play
- Tap Play Autumn at the Blue Pond in Biei puzzle to open the puzzle board, then choose your piece count and difficulty.
- Drag pieces from the tray onto the board and snap them into place until the full image is complete. Works with mouse on desktop and touch on mobile.
- Use the Preview button on the play screen to peek at the full reference image whenever you need a hint.
- When you finish, check your solve time on the completion screen and share it with friends to see who can beat your record.
Frequently asked questions
- Where is the Blue Pond, and is it natural?
- It is near Shirogane Onsen in the hills above Biei, in central Hokkaido, the northernmost of Japan's main islands. It is not a natural pond. After an eruption of Mount Tokachi in the late 1980s, erosion-control works were built along the Biei River to protect the town from volcanic mudflows, and water pooled behind one of those barriers to form the basin you see here. The pond was essentially a side effect of flood defence, and it only became a destination once photographs of it began to circulate.
- Why is the water that turquoise colour?
- Because of what is suspended in it rather than what is dissolved in it. Spring water upstream, near the Shirahige Falls, carries aluminium that reacts when it mixes with the Biei River to form very fine particles. Those particles do not settle; they stay in suspension and scatter the short-wavelength blue and green light back out of the water, while longer red wavelengths are absorbed. The result is the opaque milky blue in this photograph. The shade changes with the light and with how much sediment the river is carrying, so the pond rarely looks exactly the same twice.
- What are the bare trees standing in the water?
- They are the remains of the larch and birch woodland that grew on this ground before the barrier flooded it. The trees died where they stood when the water rose around their roots, and the trunks have stayed upright in the shallow pond ever since, stripped of bark and branches. They are the reason the place photographs the way it does — without them this would be an ordinary blue pool, and with them it reads as a drowned forest.
- When does the Blue Pond look like this?
- This is autumn, which in this part of Hokkaido means roughly the second half of October, when the larch and the broadleaf trees on the surrounding slopes turn and the first snow has already settled on the Tokachi peaks behind. The pond is worth seeing in other seasons for different reasons: fresh green in early summer, and in winter it freezes over and is lit after dark, which turns the trunks into pale shapes on a white surface. The intense blue is most reliable on a clear, calm day — overcast light mutes it, and wind breaks up the reflections that make the view work.