On 08.08.1996, Eero Savolainen observed a bright, strange phenomenon under the water surface of a small pond in Joensuu (Finland) around the reflection of the sun in the water. The colors and appearance resembled the corona, which can sometimes be observed in thin clouds in the sky. However, the crowns were not round, but had an asymmetrical shape, previously known only from pollen coronas. Therefore, diffraction by water droplets was ruled out, and another explanation was sought. On the search for further phenomena, more water coronas were quickly found. Just two days later, additional water coronas were discovered on various bodies of water. Water samples from these bodies of water were analyzed, revealing the surprising result that in two cases, the substances causing the crowns were rust fungus (spores of Chrysomyxa ledi), and in other cases, freshwater algae. Further observations finally confirmed the theory that the coronas on the water surface arise from diffraction by microorganisms.
On 19.07.1998, Heino Bardenhagen (Helvesiek) observed water coronas in Germany for the first time. Unlike the Finnish observations, which were all made in bodies of water, these coronas formed on the surface of older puddles. Continuous monitoring of these coronas revealed a dependency on the sun's height, and several conditions that favor the formation of water coronas were identified.
- The body of water must be sheltered from wind
- the ground should be clayey
- the puddle should have a high content of suspended particles and nutrients (recognizable by the dirty color of the water).
Literature on algae provided the indication that algae formation in puddles on nutrient-rich soils can often start after just 12 hours. In May 1999, special observations were made. Heino Bardenhagen observed coronas on the water surface, suspecting oak pollen as the cause. He wrote: "Directly next to the water puddle stands a young oak, about 5 m tall, which was in full bloom at the time of observation. The crown-forming substance was distributed in streaks on the puddle, suggesting airborne entry. The amount was greater near the oak. Other pollens are likely excluded, as the wind direction (west) could at most have blown birch pollen from a greater distance (about 80 m)".
If this suspicion is confirmed by water analyses at some point, pollen on the water surface could be a potential new cause of water coronas. It should therefore be noted that when observing water coronas, a water sample should be taken and analyzed for corona-causing substances.
