What changed
Miyun Reservoir in Beijing has begun its 2026 autumn fish-stocking programme, which will release 800 tonnes of silver carp and bighead carp over one month. The fish will be stocked at a 2:1 ratio, with each weighing at least 100 grams, as part of a plan to support the reservoir’s water-cleaning role.
Why it matters
These fish are filter feeders. As they grow, they consume plankton and reduce nitrogen and phosphorus nutrients in the water. That makes the stocking programme less like a simple fish release and more like an attempt to manage the reservoir as a living water-treatment system.
The plan also depends on controlling the fish population. Miyun will use concentrated fishing, catch limits and a minimum catch size of seven jin, or about 3.5 kilograms, while leaving smaller fish in the reservoir. The logic is straightforward: fish that grow too large become less effective at filtering the water, so stocking and harvesting have to work together.
The programme includes electronic weighing, video records and traceability for each batch of fish. Local authorities will also increase daytime and night patrols against illegal fishing and unauthorised angling, followed by long-term monitoring of water quality and fish communities.
The likely benefit is a more tightly managed ecological cycle, but its actual effect on water quality and fish populations will depend on the monitoring still to come.
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