Borçka Karagöl is a black lake at 1,480 metres in the mountains of Artvin, in northeastern Turkey, and nothing is holding it back. It is almost always called a landslide-dammed lake, but the geographers who mapped the slide concluded the opposite. The water covers only about three per cent of a landslide mass more than a million square metres across, a very small pond for so large a dam, and the ground between its two basins is slide debris too. The water simply settled into hollows on the rubble. Nobody recorded the year the slope came down; official sources put it in the 1800s. A wooden walkway runs the whole way round, close enough to watch the reflection change as you move, and that reflection is what the name reports: kara göl, black lake. At first light the surface usually lies under a sheet of fog, the shoreline firs fading out a few metres in, and it is gone within the hour.
Off the boardwalk the forest is Colchic, wet Caucasian woodland that takes up to 2,500 millimetres of rain a year and never fully dries. Nordmann fir and oriental spruce stand over a thicket of Pontic rhododendron and holly, relicts of a flora the ice ages wiped out across Europe and left only here and in Georgia. At the margins, trunks stand upright in the water beside you and lie half-sunk beneath it. A few are shoreline trees the lake crept up on; most of that timber comes down each winter, when avalanches off the slope to the west sweep it in. Past the end of the walkway a channel links it to a second, near-circular pool a metre and a half lower, which you will usually have to yourself. Snow shuts the only road in for about three months. And the two streams that keep the lake alive are also filling it: old surveys gave twenty-five metres of depth, and by the 2010s it was about eight. Weirs upstream and dredging are why it is still a lake and not a meadow.