Crossing the choppy and muddy estuary, they offer a sense of adventure for holidaymakers plus work opportunities and shopping choices, linking the Gironde and Charente-Maritime departments.
The westerly crossing, Royan to Le Verdon-sur-Mer, sometimes feels the swell of the ocean, and there is a salt tang to the air. Further inland, the Blaye to Lamarque line sees the ferry navigating around low, muddy islands in the middle of the river.
Elsewhere, bridges such as the 2.1km Pont de Normandie, opened after a seven-year construction project in 1995 and costing nearly €500million, have replaced water crossings.
The Gironde ferries remain partly because of the technical complexity of building bridges across the estuary and river and partly because of a deliberate political choice.
Anne-Laure Fabre-Nadler, the elected councillor of the Gironde department who oversees the ferries and other transport links, said: “If the political will was there, we could build a bridge.
“However, the cost would be very high, the environmental damage considerable and the construction work would take years.”
The Blaye-Lamarque crossing is 4km and can take between 15 minutes and 35 minutes, according to the state of the tide. Royan to Le Verdon is 6km long and takes 20-25 minutes.
Crossing from Blaye-Lamarque saves two hours by road, and Royan-Le Verdon three hours.
Upstream of the ferries is a cluster of four bridges (two road and two railway) across the Dordogne just before it merges with the Garonne to form the Gironde estuary, at Cubzac-les-Ponts, about 70km from the estuary mouth.
There are two roll-on, roll-off ferries covering the Royan-Le Verdon line, each costing about €22million, and one ferry crossing Blaye-Lamarque, which cost €11million.
Each has a crew of seven sailors and is registered as a French merchant marine ship.
They are aged 10-15 years and have a life expectancy of about 30 years. Last year, the ferries made a small profit of €120,000.Ms Fabre-Nadler said: “It is not really enough to cover emergencies, which is why we have reviewed the tariffs after a public consultation and raised those for high season, where we have the most people, and lowered them for the low season.”
Prices for a car and two people on the Blaye-Lemarque route are €16.40 one way in low season and €22.70 in high season. Royan-Le Verdon prices are €23.60 and €35.30.
“We need to look to the future and have solid finances to ensure the service continues,” said Ms Fabre-Nadler.
One million passengers a year are ferried on the Royan-Le Verdon line, which has two ships, with 250,000 on the Blaye-Lamarque line’s one ship.
Most are tourists and the holiday season is the busiest time.
There are also regular crossings by locals for work and shopping.