Navibus is the name given to a water transport service offered in Nantes. The small boats cover three lines in the Loire and Erdre rivers and carry passengers along across the river. Each line has different boats, but all accept passengers (4 in the smallest, 10 in the largest). They are owned by the same company as the tram and the stops are near tram or bus stops. The "Navibus Loire" connects Rezé and Nantes in a short 10-minute trip. The "Navibus Erdre" has 6 stops and travels along the Erdre, a tributary of the Loire. Finally there is the Navibus "Passeur de l'Erdre" which runs between Port Boyer and the university campus. It takes about 6 minutes. Tickets are sold on the boat. Personally, I don't see it as a particularly practical service, as it doesn't offer a lot of stops, but as a tourist, it's a good choice and far cheaper than the dedicated tour boats.
Quai de la Fosse is a spring of Nantes of the eighteenth century that served to link trade to the Butte Saint-Anne. In this century, it received most of the imports as one of the largest ports in France. Since its renovation, the banks are a nice place to enjoy the sun and have the perfect tan.