The Lake-men are mostly descendents of the people of Dale, the land next to the Lonely Mountain. When Smaug first took over the mountain, the people fled and many, like Bard who is a descendant of Girion of Dale, established themselves at Lake-town. The Lake-men have an established, prosperous trade system with the elves of Mirkwood. They use the river to transport and receive goods in barrels to and from the Elven-king.
When the dwarves first arrive at Lake-town, most of the Lake-men are excited about the possibility of restoring the dwarven King under the Mountain. They celebrate Thorin's return and sing many of the old songs as well as create some new ones. Many of the Lake-men feel that Thorin's return will bring prosperity and wealth back to the valley and town.