A few days ago, we took a boat tour around Sète - and it was lovely! We had the afternoon on the water, thanks to the Aquarius*.
*The Aquarius (red) goes from the port, out along the Mediterranean Sea to the Corniche and back. There are two other tours from the same company; one is dedicated to the canals (blue), the other to the étang (yellow).
They leave from the royal canal several times per day, even in winter, and cost 10-14€. The tours last on average an hour.
The commentary is in French, and there are lent booklets in English (as well as other languages)