An ethereal blue glow lights up Yundang Lake of Xiamen, east China's Fujian province, March 29, 2021. The "blue tears" phenomenon is caused by plankton named noctilucent algae, which have luciferase and luciferin in their bodies. When stimulated by waves, plankton will emit light blue. (Photo/VCG)

An ethereal blue glow lights up Yundang Lake of Xiamen, east China's Fujian province, March 29, 2021. The "blue tears" phenomenon is caused by plankton named noctilucent algae, which have luciferase and luciferin in their bodies. When stimulated by waves, plankton will emit light blue. (Photo/VCG)

An ethereal blue glow lights up Yundang Lake of Xiamen, east China's Fujian province, March 29, 2021. The "blue tears" phenomenon is caused by plankton named noctilucent algae, which have luciferase and luciferin in their bodies. When stimulated by waves, plankton will emit light blue. (Photo/VCG)