This is the 3342nd most frequent Japanese word.
放流
Release or discharge (often of water, fish, or other resources).
The word 『放流』 is used here to refer to the release of water from the dam into the river system as a controlled process.
ダムから放流された水が川を潤します。
The water released from the dam nourishes the river.
Here, 『放流』 is used in the context of introducing fish into the rivers, often for ecological restoration or aquaculture purposes.
放流イベントでは、地元の河川で魚が放されています。
During the release event, fish are introduced into the local rivers.
In this usage, 『放流』 describes the act of boats being launched or set free from the lake.