If you mean "feux d'artifice" it is fireworks. Cities and communes that have a canal or river running through it like to hold their celebrations that feature fireworks over the water, for obvious fire-related reasons. Those celebrations often require limiting traffic (not all that likely really that late at night) or parking/mooring/stationing (more likely) around the date of the event. Fireworks are pretty popular in France so you get a lot of Avis about them.
