The upper deck of the bateau-mouche "l'Hirondelle." The lower deck is usually glassed in and heated in cold weather.
This particular style of boat was used since earlier in the nineteenth century to transport freight or passengers along rivers and canals in France, but it wasn't until about 1950 that one of those boats built for the 1867 expo was used in a new venture: taking people on pleasure cruises up and down the Seine. The name "bateaux-mouches" was registered as a trademark and the business thrived, as it does today.
I've taken these cruises a few times over the years. They're really nice, day or night, especially when it's warm and you can be outside on the upper deck. There are all kinds of cruises available these days, including dinner cruises. There are also several other companies that offer similar cruises on the river, but I think the Bateaux-Mouches is the most well known.