noun
lower reaches; downstream area
Refers to the lower part of a river or valley, often in geographical or environmental contexts.
その工場は川の下流域に位置している。
The factory is located in the lower reaches of the river.
下流域では水質汚染が深刻だ。
Water pollution is serious in the downstream area.
Refers to the middle reaches of a river, between 上流域 and 下流域.
Compound of 下 (lower) + 流域 (basin, watershed).