provides an equivalent Secchi depth‘ out of the box’, allowing even the most sciencephobic diver easy access to this fascinating environmental data. The Copernicus team have also made this data available through a portal( data. marine. copernicus. eu / viewer); it couldn’ t be easier to dig into the fascinating world uncovered by our orbiting eyes in the sky.
Visibility: Mapped
Satellites, for all their promise, also have limitations, one of which is that they cannot see through clouds. As we all know, clouds are a defining feature of Britain! To get a clear view, we must either limit ourselves to those rare blue-sky days, or stitch together the transient glimpses by averaging over a longer timeframe.
Emma Taylor snorkels in a patch of thongweed
For brevity, we have chosen to average for a single month between 2010-2025; the results are shown in the map below. It’ s worth mentioning that averaging does lead to‘ smoothing’ of the data, meaning some of the finer details may be lost. It also creates a‘ fair-weather bias’ because optical satellites cannot take measurements through cloud. While poor visibility can result from offshore swells or high spring tides on a cloudless day, the most violent, sediment-stirring storms are usually hidden by cloud cover, leaving these events significantly underrepresented in the long-term averages. Even so, results remain remarkably true to our lived experience: the good and bad spots feel intuitively‘ right’. While the visibility shown is likely to be optimistic, the trends are valid.
Variation of average water clarity around the UK for May 2025
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