China's third-largest hydropower station began to store water on Wednesday, slightly affecting the water level of the river it straddles.

The Xiangjiaba Hydropower Station, spanning the Jinsha River, a tributary of China's longest river, the Yangtze in the southwestern Yunnan and Sichuan provinces, has been recording rising water levels in the reservoir since the commencement of the water storage at around 9 a.m..

The water level is expected to rise to 354 meters from the current 280 meters in five to seven days, according to local hydraulic experts.

The power station, with a total installed capacity of 6.4 million kw, is scheduled to be operational this year. Upon operation of all generating units, the annual electricity output of the plant is likely to reach 30.7 billion kw-hour.

The water level in the Three Gorges Dam, the world's largest water control and hydropower project lying in the upper reaches of the Yangtze River, dropped by 0.04 meters six hours after the water storage began.

Xiao Ke, a senior official with the Three Gorges project, said the slight drop "was expected."

"In the following days, the water flow into the reservoir will keep decreasing and it will finally stabilize at 15,000 cubic meters per second, because of the water storage of the Xiangjiaba Hydropower Plant," he added.