From Longman Dictionary of Contemporary Englishheadwatershead‧wa‧ters /ˈhedwɔːtəz $ -wɒːtərz, -wɑː-/ noun [plural] SGthe streams that form a river
Examples from the Corpus
headwaters• The 325-acre fen, headwaters of the Waveney river, will be designated a national nature reserve.• He did not know that Henry Schoolcraft had discovered the headwaters four years before and far to the north.• In the headwaters of most rivers there are large tracts of agricultural land and a virtual absence of industrial discharges.• The highest of the mountain ridges separated the headwaters of the Belpan and Makaa.• Fish moved from the lower parts to the headwaters soon evolve local ways. 