anabranch

n. [ Anastomosing + branch. ] A branch of a river that reënters, or anastomoses with, the main stream; also, less properly, a branch which loses itself in sandy soil. [ Australia ] [ 1913 Webster ]

Such branches of a river as after separation reunite, I would term anastomosing branches; or, if a word might be coined, anabranches, and the islands they form branch islands. Col. Jackson. [ Webster 1913 Suppl. ]