The sixth stage took us out of Auvergne and into the Midi-Pyrénées to the town of Montauban, on the Tarn river and home to the Canal de Montech, part of the Canal de Garonne, itself part of the massive Canal des Deux Mers along with the Canal du Midi, which we’ll meet again on Stage 10. At Montech on the Canal de Garonne, there is a very strange contraption called a water slope.

A water slope is an alternative to locks in a canal. A lock usually works something like this

That is, a boat goes in at one level, the lock fills up and the boat leaves at another level. The water slope was invented by Jean Aubert as an alternative and installed at Montech and Fonserannes. I can’t seem to find a good GIF, but here’s a video of the water slope at Fonserannes.

There is a concrete slope built on a hill. The boat enters the slope at the bottom of the hill and a gate is closed behind the ship, locking in a wedge of water underneath the boat. This confused me a bit at first, but the boat is sitting on flat water. The hypotenuse of the triangle is on the concrete slope. The gate is then pushed up the hill by railroad locomotives, carrying the wedge of water up with it. When it reaches the top, the water is now level with the rest of the canal and the boat can sail away.

Ingenious, isn’t it? Well, there’s probably a reason why only two of them were ever built. Still, the extensive canal network in the southwest of France is a marvel, and one that we’ll return to when we cross the Canal du Midi in a few days.

Another sprint finish in Montauban on the banks of the Tarn, pulled out at the last second by Mark Cavendish, with a surprise third place from the British newcomer Dan McLay.

And if you ever wanted to watch a 20 minute video of an inactive water slope from a drone, you’re in luck.