Collins COBUILD Advanced Learner's English Dictionary - reaches

1. The upper, middle, or lower reaches of a river are parts of a river. The upper reaches are nearer to the river’s source and the lower reaches are nearer to the sea into which it flows. This year water levels in the middle and lower reaches of the Yangtze are unusually high. N-PLURAL: usu the adj N of n 2. You can refer to the distant or outer parts of a place or area as the far, farthest, or outer reaches. (FORMAL) ...the outer reaches of the solar system. N-PLURAL: usu the adj N of n 3. You can refer to the higher or lower levels of an organization as its upper or lower reaches. (FORMAL) ...the upper reaches of the legal profession. = echelons N-PLURAL: usu the adj N of n