The origin of the color of the Wörthersee
"The beautiful turquoise blue coloration of the Wörthersee but also of many other lakes depends on turbidity, algae content and on the scattering and absorption of light in the water. The colors of the surroundings only seem to influence the water coloration by reflection.
Especially in the summer months, Lake Wörthersee has a whitish to turquoise turbidity. The color is caused by the finest lime particles (calcium carbonate). Among other things, lime is carried into the lake by the lime-rich Alpine tributaries. Directly in the lake, lime is formed with the help of algae. The algae need carbon dioxide for photosynthesis. If algae growth increases, carbon dioxide becomes scarce. Then the hydrogen or bicarbonate, serves as a carbon source for building organic matter. The building of organic matter from carbon dioxide and water using solar energy is called assimilation. With the consumption of carbon dioxide or from the use of bicarbonate as a carbon source, the pH of the lake water increases, with the result that the balance between calcium hydrogen carbonate and carbonic acid shifts and lime is formed. This agglomerates into differently shaped crystals and aggregates, the calcites, and precipitates. This process is called biogenic decalcification. Put simply: because suspended algae extract carbon dioxide from the lake water as they grow, lime precipitates in the form of very fine lime particles.
The light of the sun also determines the color of the water. The sun penetrates the water with its rays, or its rays are reflected on the water surface. The portion of the light that is reflected results in the color of the water. This process is called selective transmission. Short-wave light (blue) is much more dispersed and reflected the most, so pure water appears blue from above in greater thickness. Deep blue water also contains little suspended matter that would alter the blue color.
In calcareous waters such as Wörthersee, Faaker See and Weißensee, the scattered light is reflected by the small, scattered lime crystals in the water, the scattering effect is intensified and the water appears turquoise blue. If these lime particles sediment in the shore regions, the white-blue lake chalk banks visible from afar are formed.
Blue water colors occur only in water bodies with low organic production, because plant plankton (algae) makes the water appear in a wide variety of green to yellow-brown or even blue-green shades."
