What is the main conflict in Caddie Woodlawn by Carol Ryrie Brink?

It is 1864, and the settlers near Dunnville, Wisconsin, on the Menomonie River, are nervous and isolated. Only two years earlier in Minnesota the Indians had killed a thousand settlers, and their own vulnerability makes the settlers in Wisconsin nervous. Caddie, her dog Nero, and her brothers Tom and Warren do not share that nervousness. Although they cannot swim, they cross the river — the other two clinging to Tom’s shoulders as he tiptoes along the riverbed. They watch the Indians working on a birchbark canoe, then head home, stopping to forage for hazelnuts.