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The chromatic SOS of lakes

How and why freshwater lakes change colour

Marta Abbà
a story by
Marta Abbà
The chromatic SOS of lakes

Those who photograph them enthusiastically may not know that lakes dye from heavy rainfall and turn pink or green from unexpected droughts and the action of algae and bacteria. Effects of the climate crisis and environmental pollution, to which art tries to give voice

Masazir in Azerbaijan, Dusty Rose Lake in Canada, Torrevieja in Spain, Pink Lake in Australia: more and more lakes are changing colour. Understanding how and why is not trivial but necessary, to try to restore each lake’s ecosystem balance

Pink lakes and not-so-pink scenery 

A singular example is in Senegal: the Retba Lake, pink since time immemorial, is a source of great pride but above all a source of income for those who support themselves through agriculture or tourism from its shores. Increasingly frequent heavy rainfall and sewage runoff from surrounding neighbourhoods have increased its level from three to six metres. Even those who have only used poster paint “that one time at school” can see how the lake has lost its colour and the inhabitants of the shores their basic source of livelihood. 

This episode1 is counterpointed by many others, in which the appearance of the lake pink, on the contrary, is by no means a sign of good health. This is the case, for example, of Lake Hillier in Australia, which has recently seen its level drop dramatically, turning pink due to the concentration of almost five hundred bacteria, algae and viruses. Unexpected hosts, known as extremophiles, possess the ability to thrive in conditions that are considered extreme for most organisms, as well as the surrounding environment. These conditions, exacerbated by prolonged and unprecedented droughts, have become their habitat.

Remember poster paint: if there is no water, the colour becomes more charged, because the salinity level increases, causing organisms such as the microalga Dunaliella salina,2 one of the few in the world that tolerates sodium chloride concentrations of up to 35%, pH of up to 11 and temperatures of up to 38 °C, to proliferate.

The presence of Dunaliella salina spells trouble for a lake that used to be fresh, as does that of Salinibacter ruber, a bacterium used to live in extreme concentrations of salinity (20%-30%). Both turn the water pink to protect themselves from radiation and ultraviolet rays: Dunaliella by increasing the production of beta-carotene, Salinibacter that of bacteriorhodopsin, both natural “colourants”. 

Change colour, same message: we are in crisis 

Other freshwater mirrors (or nearly so) have opted for less “pop” colours, exploring shades of green or blue more explicitly linked to a state of “climatic malaise”. 

In the Great Lakes area of North America, Lake Erie, which had turned greenish, was observed by satellite by the NOAA-National Oceanic and Atmospheric Association, which also took samples to measure its toxicity3

Even in North China, when Lake Hulun4 urned dark green, it was promptly checked to quantify the concentration of certain special organisms: cyanobacteria.

Wannes Van Hassel is a biochemist by training. After his Master’s degree at KULeuven, he obtained a PhD in ‘Science’ at the University of Liège and a PhD in ‘Food Science Engineering’ at the University of Ghent, developing a method to quantify cyanotoxin in the Belgian food chain in collaboration with Sciensano, a public health research institute where he currently works, in the ‘Toxins’ unit.

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«The discolouration of lakes caused by cyanobacteria is a worldwide phenomenon that affects all living things and is likely to become increasingly frequent, with even more persistent episodes,» explains biochemist Wannes Van Hassel, who has been studying the blooms of these single-celled organisms for years, which can turn lakes green, bluish, yellow or red. Each species contains a different coloured layer of foam or slime, depending on the mix of pigments, but the cause of their proliferation is always the same: climate change.

«When temperatures rise and consequently the number of their nutrients such as phosphorus and nitrogen also increases, optimal conditions for the proliferation of cyanobacteria are created,» explains Van Hassel. «These same conditions can also be caused by the eutrophication of lakes5 caused by agriculture or industry».

The problem, the professor points out, is not related to the colour pigments they produce in lakes but «to the increase in their biomass in the water, which can have negative effects on the entire ecosystem: when cyanobacteria aggregate at the surface, they overshadow deeper photosynthetic organisms and take oxygen away from other life forms». There is no shortage of health damage: «Some cyanobacteria can also produce toxic compounds that can damage the nervous and gastrointestinal systems, as well as the kidneys and liver, in humans and other animals,» Van Hassel points out.

The colour of denunciation: the works of Shigeko Hirakawa 

The scientific community speaks clearly, but sometimes the message does not get through as effectively as hoped. This is where artists come in, those artists who for more than 10 years have chosen to help lakes express their discomfort by putting them at the centre of their works.

Shigeko Hirakawa is an environmental artist. Born in Japan, she has lived and worked in France since 1983, where she arrived thanks to a scholarship. As a painter, she became interested in the relationship between man and nature, creating en plein air installations on themes such as water, air, solar energy, plants and ecosystems. Her works have been shown in various exhibitions, mainly in France, Japan, Belgium, Switzerland and the USA.

Discover her artworks

Some do just that using colour, but not algae or bacteria. For example, Shigeko Hirakawa, a Japanese-born “climate performer” working in France, has focused on fluorescein, a biodegradable and harmless red-to-orange powder that turns water green and has been used as a natural fluorescent dye since 1960: considered by the WHO as a valid diagnostic tool in the field of ophthalmology, it is also used to ‘trace’ groundwater.

In her work Follow the Water (2014), Hirakawa coloured the waters flowing through 83 hectares of garden at the Château de Trévarez in Brittany to confront us with the enormity of our water consumption.

follow the water shigeko hirakawa
A drawing of the work Follow the water with the path of water coloured by the artist inside the Château de Trévarez estate (France, Normandy). Source: Shigeko Hirakawa. All rights reserved. Reproduced with the artist’s consent.  

«The idea came about in 2012 while reading a UNESCO report and a study by the University of Netherlands6 on the annual global and French water footprint,» the artist explains. French water consumption figures, 1800 tonnes of water per year, 97% had “unexplained” causes: «Looking at the numbers carefully, I realised that we cannot control water wastage at the private level, but we certainly can and must do so at the political level», says the artist. 

«The amount of water in the reservoir of the château’s water system coincided exactly with the water footprint of a Frenchman: with my performance, I coloured it to make people visualise the impressive amount of water they consume and made it flow through the channels of the estate, down to the lake located at the bottom of the garden, gradually turning it bright green», she explains. «I also coloured that of the basin next to it, in an amount equivalent to Ethiopia’s water footprint: together, the basin and the lake contained 2,500 tonnes of coloured water or the individual water footprint of the United States». A journalist who visited the work soon went from amazement to astonishment as she reflected on individual and collective water consumption. 

Some shots of the installation “Follow the water” in the Château de Trévarez garden (France, Normandy), with a detail of the flow of water coloured with fluorescein towards the basins located in the lowest part of the garden. Source: Shigeko Hirakawa. All rights reserved. Reproduced with permission of the artist.

Next to Follow the Water, Hirakawa installed Water in a Bubble: 9 plexiglass spheres with a diameter of 40 cm placed on one of the basins in the castle garden, in the 90-metre wide ‘Hunter’s Basin’. Thanks to a slit in the lower part of the basin, the fluorescein from Follow the Water also coloured each of the Ball of Water green: «inviting observers to consider fresh water as a precious resource in the whole planet and not to be wasted» specifies Hirakawa. «Although in some areas it may seem to be available without quantity limits, this is not the case».

The Water Footprint (2014) installation in the same area also emphasises water waste, again based on UNESCO water consumption data: Hirakawa collected in a tank an amount of water equal to that consumed by an average person in one day (55 tonnes) and created an elastic, walkable walkway almost 25 metres long and six metres wide. «It was necessary to walk through it barefoot and one by one, to better perceive the fragility of this resource and, at the same time, fully realise the considerable amount of water we consume every day, ignoring its value» the artist explains. 

Shigeko Hirakawa is still working on this theme: his next work, Water Cycle – Gaïa and Cyclops will focus on the relationship between the water cycle and climate change, to continue to give shape and voice to that SOS that in turn does not cease to give colour to lakes, in every part of the world.  

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  1. Evidence of rescue restoration of Lake Retba, Diaw, P. A. (2023, February 1). Lac Rose au Sénégal : quelle solution pour lui redonner sa fameuse coloration ? BBC News Afrique. ↩︎
  2. On the ability of Dunaliella salina to adapt to extreme salinity levels see Oren, A. (2014). The ecology of Dunaliella in high-salt environments. Journal of Biological Research – Thessaloniki, 21(1). On the future of this algae, marked by the climate and anthropisation crisis, see Ramos, A. et al. (2011). The unicellular green alga Dunaliella salina Teod. as a model for abiotic stress tolerance: Genetic advances and future perspectives. In ALGAE 26(1):3-20. 10.4490/algae.2011.26.1.003. ↩︎
  3. Monitoring details on Lake Erie – NCCOS Coastal Science website. (2024, April 10). In NCCOS Coastal Science Website.↩︎
  4. On the history of Lake Hulun see Chen, X., Chuai, X., Yang, L., & Zhao, H. (2012). Climatic warming and overgrazing induced the high concentration of organic matter in Lake Hulun, a large shallow eutrophic steppe lake in northern China. In Science of the Total Environment, 431, 332–338. ↩︎
  5. Eutrophication means the growth of plant organisms due to high doses of nutrients such as nitrogen, phosphorous or sulphur in the aquatic ecosystem, from natural or anthropogenic sources (such as fertilisers, certain types of detergents, domestic or industrial wastewater). See Giorgi, G., PennaIstituto, M. (2023). Eutrofizzazione. In Istituto Superiore per la Protezione e la Ricerca Ambientale.↩︎
  6. The report “The Water Footprint of humanity” (Hoekstra, A. Y., & Mekonnen, M. M. (2012). The water footprint of humanity. In Proceedings of the National Academy of Sciences of the United States of America, 109(9), 3232–3237. and focus on France from which the artist drew the data for her works (Ercin, A. E., Mekonnen, M. M., & Hoekstra, A. Y. (2012). The water footprint of France. In Value of Water Research Report Series (No. 56). UNESCO-IHE Institute for Water Education. ↩︎


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