Lian Feng, Xuejiao Hou, Junguo Liu, Chunmiao Zheng

Given its advantages for synoptic and large-scale observations, satellite remote sensing has been widely used to effectively monitor the water quality of inland and coastal environments. Using satellite-derived reflectance data from the Landsat 5 Thematic Mapper (L5TM) as a proxy for algal bloom intensity, Ho et al. 1 showed an increase in peak summertime bloom intensity in 68% of the 71 large lakes worldwide from 1982 to 2012. However, we question the veracity of their finding for at least two reasons: (1) satellite-derived reflectance in a single near-infrared (NIR) band is not a reliable proxy for bloom strength due to the strong impacts of suspended sediments and aquatic vegetation, and (2) the infrequent satellite observations from L5TM (one cloud-free image every 1-2 months) make it difficult to draw statistically meaningful conclusions. Therefore, although it is natural to speculate that more blooms may be found in lakes under changing climatic conditions, the work by Ho et al. 1 needs to be revisited before reaching any solid conclusions.