The Chambeshi (or Chambezi) River of northeastern Zambia is the most remote headstream of the Congo River (in terms of length) and therefore considered its source. (However, in terms of volume of water, the Lualaba River is the greater “source” of the Congo.)
The Chambeshi rises as a stream in the mountains of northeast Zambia near Lake Tanganyika at an elevation of 1760 metres above sea level. It flows for 480km into the Bangweulu Swamps, which are part of Lake Bangweulu, and by the end of the rainy season in May, it delivers a flood which recharges the swamps and inundates a vast floodplain to the southeast, supporting the Bangweulu Wetlands ecosystem. The water then flows out of the swamps as the Luapula River.
For more than 100 km of its length as it flows to the east of Kasama the river consists of a maze of channels in swamps about 2 km wide, in a floodplain up to 25 km wide. Further downstream, where it is bridged by the Kasama-Mpika road and the Tazara Railway, the permanent main channel is about 100 m wide, and up to 400 m wide in flood.
The above story is based on materials provided by Wikipedia