Abstract: Invasion and biofouling of golden mussel (Limnoperna fortunei) in the pumped-storage plants (PSPs) in China has caught wide attention. The specific operation mode of PSPs is regarded as the major cause for golden mussel biofouling in water intakes and tunnels, and particularly, the cooling water systems of PSPs usually consist of small tubes under high risk of being clogged. This study aimed to find a relationship of variations in the density of golden mussel veligers versus the daily operation of Langyashan PSP, located in a tributary watershed of the Yangtze in East China. Such a relationship is generally helpful in adjusting daily operation to avoid the biofouling in tunnels and structures. We have conducted a series of continuous in-situ observations in the peak veliger reproduction season. The results showed that the density of veligers near water surface increased with water pumping operation time and decreased significantly with stop time. And a similar effect of pump operation time was detected on the densities at different water depths. Normally more planktonic veligers existed in the shallow water layer, but during longer stop time, most of them sank down to the reservoir bed and probably were killed there by sediment falling and insufficient oxygen owing to little water flowing disturbance.