We are eight in all, careening in an unventilated box along dirt roads above the Geiseltalsee, the Hostage Valley Lake, a former brown coal mine and Germany’s largest artificial body of water. Our tour guide, Herr Hossfeld, whom I call Hoss, would suggest we go swimming in the 423 million cubic meters of cool water below were it not still illegal to do so. Even then, we would have to scramble over two fences and cross a rocky beach. Trouble is, the Hostage Valley Lake is behind schedule.

Hoss is too busy fielding questions from the group on this very theme to comment on the wonders of a new solar farm, or on the expansive man-made levee we are crossing that separates the polluted lobe of the mine from the massive, flooded, unpolluted area.

…I wonder: shouldn’t such precision reassure, not frighten? If one can measure a problem, can one not solve it?

“What about underwater landslides?” one woman asks. “What about subsidence?”

“No, no,” Hoss says. “It is safe.” He is standing facing us, bobbing with the rocking of the truck. “Gottes willen,” he whispers, wiping his forehead dry. God forbid.

“Is it true the lake may never fill because of seepage and evaporation?” The question lingers as billions of euros of engineered earth and a stranded marina pass by outside the truck’s windows. “Yes,” he says calmly, surfing with the truck’s movements.

We arrive at our first stop: this is the pumping station. It is nearing half past two in the afternoon, 100 degrees, and one tour member opens a bottle of red wine and distributes white plastic cups. I pass up the wine and inspect a high-tech lock system built between the shore of the lake and a lush creek bed where the Geisel stream trickles away toward sleepy villages. The creek is vestigial, what little remains of the admittedly modest Geisel river before it was erased to mine brown coal, huge amounts of brown coal, discovered here in 1698. The locks are there to someday feed the Geisel its water once more. But as Hoss goes on, it begins to seem like the locks will never be opened.

“At a recent meeting,” he says, drawing his free hand back through matted gray hair, “it was pointed out that the ongoing heat wave had already taken one centimeter off the lake.” Losing one centimeter might not seem like much, but when that loss is from 11.5 square miles of water that are supposed to be rising, it is unsettling. One woman in the group actually gasps. At the same time, I wonder: shouldn’t such precision reassure, not frighten? If one can measure a problem, can one not solve it?

Faded, laminated photographs are distributed by the tour driver, Herr Steinfelder. They depict the initial moments when water began being pumped in from the Saale river. The old mine was vast and dry and looked like the Sonoran Desert with a huge mushroom of pure water erupting inside. There is something almost lurid about the water against the tawny dirt, something panicky and vulnerable about the gushing captured on film.

Now, with the lake nearly filled, it is clear what would happen if they stopped the pumping. It is a hydrological necessity if the beaches and two marinas and nature preserve and tourist economy are to take root, from scratch, as planned, in this old brown coal mine. Because of seepage, pumping will continue for at least twenty years. People are beginning to worry the unavoidable state of this man-made valley might be more like the faded picture of the desert than a water wonderland.