A shoal of koi carp swarm a half-frozen lake in Yuanmingyuan, or the Old Summer Palace, in Beijing, capital of China, Jan. 18, 2021. (Xinhua/Yin Dongxun)

A shoal of koi carp swarm a half-frozen lake in Yuanmingyuan, or the Old Summer Palace, in Beijing, capital of China, Jan. 18, 2021. (Xinhua/Yin Dongxun)

A shoal of koi carp swarm a half-frozen lake in Yuanmingyuan, or the Old Summer Palace, in Beijing, capital of China, Jan. 18, 2021. (Xinhua/Yin Dongxun)

A shoal of koi carp swarm a half-frozen lake in Yuanmingyuan, or the Old Summer Palace, in Beijing, capital of China, Jan. 18, 2021. (Xinhua/Yin Dongxun)