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Choose a lake
checked weekly, with pictureshistorical record onlytoo small for 20 m pixels
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One lake, seen from 786 km up
Sentinel-2, 10 m pixels…
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The record, gaps included
The readings and lab values as a table
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What the record shows so far
exploratory, on data already examined5
What it cannot tell you
- It is not a test for harmful algae or toxins. The index responds to green pigment and plant material. It cannot tell blue-green algae (cyanobacteria) from harmless algae or weed, and it measures no toxin.
- It is not swimming advice. For a bathing water, the Environment Agency's own notices and signs on site come first. SwimSignal shows those notices on each spot page.
- A cloudy day is unknown, not clean. When no clear image exists the record has a gap. Nothing is filled in between readings.
- It sees 300 m of open water, not the whole lake. Blooms often gather at shores and in bays the reading does not cover.
- The units are not chlorophyll. No conversion from the index to µg/l has been validated. Lab values are shown on their own scale.
- October readings are experimental. The index was compared with lab chlorophyll only from May to September.
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