Aoiike Blue Pond (Biei)

LakesHokkaido, Biei,Japan

An accidental pond on Japan's Hokkaido behind a volcanic mudflow dam, its milk-blue water coloured by dissolved aluminium, with drowned larches standing in plantation rows.

September·Edge of season

Aug–Sep

Late-summer downpours and the odd typhoon flush river silt in and cloud the water milky for days, as after the August 2016 storm, before it clears on dry spells. Broadleaf colour builds by late September.

Year-round The bleached larches stand year-round; the water is blue whenever the river runs clear, and vanishes under snow in winter.

Aoiike is a small pond of opaque milk-blue water with dead larches standing up out of it, bleached and branchless, lined up in rows too neat for a wild forest. The slope they grew on was a plantation, and the water drowned them. The colour is real, and it is chemistry. Groundwater rising around Shirahige Falls upstream carries dissolved aluminium, and where it meets the river it forms particles of aluminium hydroxide so fine that they scatter the short blue wavelengths out of sunlight. It is the same physics that makes the sky blue. The pond itself is an accident. After Mount Tokachi erupted in December 1988, engineers dammed the Biei River with a line of concrete blocks to catch volcanic mudflows before they could reach the town, and water pooled behind the barrier. What no photograph tells you is how often the blue is missing. Snowmelt and heavy rain dilute the water and flush river silt into it, and after a typhoon in August 2016 the pond ran brown for weeks and closed. The colour is deepest in June and October, when the meltwater is gone and clear days are common, and it needs direct sun. At dawn the surface goes to glass; by midday the turquoise reaches full strength. In late October the larch behind the pond turns amber and the first snow usually lands on it while the water is still open. That is the frame Kent Shiraishi shot and Apple shipped as a Mac desktop in 2012, which is why the view is familiar before you ever arrive. Then winter takes it: snow buries the surface, the blue is gone until spring, and the town lights the bare trunks after dark instead.

Worth knowing

Good to know

Give the pond two or three dry days after heavy rain — silt washes down the river and the blue goes milky. It clears on its own, but not overnight.
Come at opening rather than after breakfast — the car park opens early from May to October, and the coach tours land mid-morning. The first hour is the quiet one.
In winter, plan for dusk, not noon — the lights are on the trees, not the water, and they run nightly until 21:00 from late October to late April.
Stay on the marked path — leaving the viewing area or entering the water is banned, and the town warns that the ground beyond the rope is genuinely dangerous.

Things to do

1
Wait for the trunks to meet their own reflections
At first light the surface goes to glass and the dead larches stand doubled, hard to tell from their reflections. Stay a few hours and the colour moves under them, swinging from turquoise to grey-green as the sun climbs and the light angle changes.
2
See the buried pond lit after dark
From December there is no water to look at — ice and snow have taken it. The town lights the bare trunks instead, working through a slow cycle of white and blue from points set around the bank. In winter you photograph the pond's skeleton, not the pond.
3
Walk the bank and find the plantation rows
The short path along the water's edge keeps re-stacking the trunks: a random thicket from one angle, then suddenly the straight rows of the forestry plot they once were. Where the water is shallow and clear you can follow the trunks on down under the surface.
4
Follow the blue upstream to Shirahige Falls
About 2.5 km up the valley, groundwater bursts out of the cracks in a cliff face and drops into the Biei River — this is where the aluminium enters the water. From the bridge above, you can see the river running the same impossible blue, and the pond's colour being made.