also: いせき
noun
A structure built across a river or stream to control water flow, raise the water level, or divert water. Often used in irrigation, flood control, or water supply contexts.
川に堰を作って、農業用水を確保した。
They built a weir across the river to secure irrigation water.
堰を開けて水を流す。
Open the sluice and let the water flow.
Rare kanji form; the reading いせき is uncommon and may be encountered in historical or technical contexts.
ダム is a large-scale dam for water storage or power generation, while 堰 is often a smaller barrier for controlling or diverting water flow.
The kanji 堰 is a phono-semantic compound: 土 (earth) + 匽 (phonetic, also meaning 'to block'). The reading せき is the native Japanese kun'yomi.