The EyeOnWater website and adjacent free Apps help you to assess the Colour and Clarity of natural waters and the physiological state of Ulva (Sea Lettuce).

EyeOnWater - A visualisation of scientific data shared by the community

People have always been interested in observing their surroundings. Whereas observation satellites and in-situ measuring stations are set up to monitor vast areas of ocean coastlines, this can now be complemented by EOW Colour, Clarity and Sea Lettuce (Ulva) observations carried out by citizens.
Data will be used by scientists (oceanographers, limnologists) and water authorities for statistical and long-term analysis in conjunction with climate research.

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Join the community, download the apps:


The EyeOnWater colour app helps us to classify rivers, lakes, coastal waters, seas and oceanc on it colour (it can be used over both fresh and saline natural waters). The observations via the app are an extension of a long term (over 100 years) set of water colour observations made by scientists in the past. You can view them all together in this map application. If you have contributed yourself, do not forget to login for a more personal experience.

View the map of colour observations


Ulva lactuca (sea lettuce) belongs to the green seaweeds and can be found worldwide along shores of seas and oceans.
Ulva"s color can range from pale-green to dark-green, and the color is most likely linked to the nutritional and/or physiological status of the seaweed.

Map of Ulva observations coming soon!


Clarity observations are usually done by Secchi Disk, lowering a white disk in the water and measuring to what depth it is still visible. EyeOnWater has collected a large dataset of observations from the past, and this set has been extended by citizens and volunteer measurements contributed via the EyeOnWater app.

View the map of clarity observations
Eyeonwater APP