Canal de Bourgogne: St. Florentin to Tonnerre

Fosse Dionne

Fosse Dionne

Wanderlust’s next stop along the Canal de Bourgogne was Tonnerre. The French word “tonnerre” translates as “thunder” in English, though rumblings from the sky do not appear to be the inspiration for the commune’s name. In truth the name alone might well have prompted us to visit. We have a low bar for such things. But there is more to recommend Tonnerre than its name. The commune has two star attractions, Fosse Dionne and the Hotel-Dieu de Tonnerre. Curious name or not, it is a worthy stop for those traveling in the area by boat, car, train, or bike.

In French-speaking countries an hôtel-Dieu or “hostel of God” refers to hospital for the poor and needy, run by the Catholic Church. These weren’t hospitals in the modern sense. Many patients did not check in to an hôtel-Dieu and expect to leave. An hôtel-Dieu was often about providing comfort and support to the sick and dying. They were hospices that prepared the souls of the sick for the afterlife. A visit to a historic hôtel-Dieu is a reminder of the suffering and pain of death and illness in the Middle Ages.

Some facts: According to Wikipedia, Tonnerre’s hôtel-Dieu is the longest medieval hospital in Europe. Though we did not pull out the tape measure and verify the record, we can confirm that the inside is indeed cavernous. Wikipedia also notes that the Hôtel-Dieu de Tonnerre is amongst the oldest hôtel-Dieu in Europe. It was founded in the late 13th Century. That being said, in Europe old is relative. The Hôtel-Dieu de Paris was founded in 651, over 600 years before the hôtel-Dieu in Tonnerre. As a comparison, Columbus sailed the ocean blue a mere 524 years ago.

Hôtel-Dieu de Tonnerre

Hôtel-Dieu de Tonnerre



Fosse Dionne is a secular and more unusual attraction. The ancient wellspring at the base of a hill in Tonnerre has provided water to humans for millenniums. It became the logical focal point around which a settlement formed. In Roman times the area was developed utilizing the spring as a source of clean water. This settlement ultimately became the commune of Tonnerre. .

In 1758 Fosse Dionne was transformed into a lavoir, the form that can be seen by visitors today. A lavoir or washhouse is a place for the cleaning of clothes. Lavoirs are a common sight in this area of Burgundy. Many local communities have preserved and maintained their lavoirs, which typically date from the 18th and 19th Centuries. (We’ve actually seen one in use on the Canal du Midi, but that is unusual.) Along with being a place to wash clothes, lavoirs also played an important role as centers for the social life of the townswomen. As the clothes were being cleaned important news and gossip were exchanged.

A sign at Fosse Dionne says that the spring divers have explored 300 meters.

A sign at Fosse Dionne says that divers have explored inside the spring for 300 meters.

A lavoir alongside the Canal de Bourgogne

A lavoir alongside the Canal de Bourgogne

What makes Fosse Dionne special is the amount of water that the spring produces. Over a 20-year observation period, the flow was found to vary from a peak average of 619 liters per second in January to a minimum of 87 liters per second in August. When we visited in July of 2016 the flow was likely near the lower end of the range. Still, 87 liters/sec converts to nearly two million gallons of water a day. It’s a lot of water. The volume of the flow undoubtedly contributes to the pool’s deep blue green color.

Mooring Wanderlust in Tonnerre came with a little adventure. Midway through our stay I realized that we were grounded at the skeg, the lowest part of the boat that serves as a support for the bottom of the rudderstock. Apparently in the process of reversing the propeller to tighten the mooring lines, we lifted the back of the boat as we stretched the ropes going backwards. When the throttle was cut we unknowingly dropped the skeg onto some unidentified object under the water at the end of the quay. Later, a boat passed through the lower lock of the short pound that holds Tonnerre’s port. This dropped the water level a few inches. It was enough to hold Wanderlust solidly. No amount of thruster or throttle would make her twitch. If we wanted to we could have pulled in all of the mooring lines and Wanderlust would have just stayed fixed in place.


Fosse Dionne: The low roof covers the clothes washing areas.

Fosse Dionne: The low roof covers the clothes washing areas.

By chance I first noticed that we were hung up when I checked the level of the floor in the saloon with a spirit level. The level showed that the floorboards were level. Very odd as under normal circumstances the floor’s slope would normally have been around 2% to the stern. At the time the freshwater tank at the bow was nearing empty. If Wanderlust’s water tank is empty the bow floats up and the stern is pushed deeper into the water. If anything, the floor’s slope should have been more than 2%. In any event we figured that if we filled the freshwater tank it might take enough pressure off the skeg to free Wanderlust. But it didn’t help. Even with a full tank of water at the bow we still wouldn’t budge. We were impressively stuck.

Our only hope was to appeal to the VNF, Voies navigables de France, the French authority that manages navigation on the inland waterways. With hand signals and a few words of French we requested that the VNF raise the level of the port’s pound. On the day of our departure, the VNF complied. A feed water gate was opened and the pool between the two locks was filled until the water lapped over the top of the lower lock gate.

Wanderlust stuck at the quay with her stern lifted. It looks like a concrete block may extend away from the bank.

Wanderlust stuck at the quay with her stern lifted. It looks like a concrete block may extend under the water away from the bank.

With a short blast of the throttle Wanderlust moved forward off whatever she was held by. I looked back to the stern trying to see the mystery underwater object that had held Wanderlust fast but the water was murky. We still have no idea what the skeg was on under the water. In any event, Wanderlust was free to leave Tonnerre without so much as a clap of thunder.


It’s about 26 kilometers with 11 locks by canal from St. Florentin to Tonnerre. Wanderlust made this passage on the 15th of July 2016. Her engine ran for 7.1 hours. We spent four nights at Tonnerre’s port de plaisance.

Click here for a map of the route.


There is something under the water here that Wanderlust was stuck on.


2 thoughts on “Canal de Bourgogne: St. Florentin to Tonnerre

  1. Pingback: Canal de Bourgogne: Tonnerre to Tanlay | Wanderlust

  2. Pingback: Canal de Bourgogne: Troubles in Ancy-le-Franc | Wanderlust

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