WUHAN, June 21 (Xinhua) -- The Three Gorges reservoir, the largest water control facility in the world, has started its second project this year to stimulate fish spawning in the Yangtze River.

The week-long operation started Sunday. The outflow of the reservoir was 11,000 cubic meters per second on the first day, and was increased by 1,000 to 1,500 cubic meters per second every day until Saturday.

Spawning of the four major Chinese carp -- black carp, grass carp, silver carp and bighead carp -- usually happens when two conditions are satisfied, appropriate water temperature and rising water levels.

The reservoir has carried out 12 such operations since 2011, which have greatly stimulated natural propagation of carp.