To the Caño Cristales, the most colourful river in the world
Many know the Caño Cristales from documentaries on TV. Its red plants have become world-famous. Perhaps also because biologists from all over the world are faced with a riddle: The plants that give it the name "Liquid Rainbow" are red in one part of the river and green in another.
The zoo river
Every morning the tour starts in the small village of Macarena. We walk to the river and then go by boat for about 30 minutes to a jetty, from where we walk to Cano Cristales or Cano Cristalito. These walks were up to 15 km long. The river, however, was something very special. To the left and right of the bank, various species of animals were basking in the sun, which we had either not seen before or only seen from a great distance. However, the animals seemed to be used to boats and let us get very close. Ideal for the photographers in the team!
Finally at the most beautiful river in the world
It is the plant Rhyncholacis clavigera that gives the river different colours from July to November. It starts as a green plant, changes to yellow to red and even sometimes to purple. In November, it starts to produce flowers, which then scatter their seeds during the following dry period. However, it is unclear why only some plants develop the red colour and others do not. The plants are extremely adapted to the strong current in the river. Their roots claw at the bare rock and their soft, fine-fibred structure offers little resistance to the water.
Since the water of Caño Cristales and Caño Cristalito is extremely clear, it’s very good for fish observations in the warm water of around 26-28 °C. The limited number of fish species makes it no less exciting. We were particularly taken with the endemic dwarf cichlid species Apistogramma alacrina. The breeding females display a beautiful yellow colour! It was interesting to note that the apistogrammas were always found in calmer areas of the river. They were never to be found in stronger currents.
Because of the red plant colour, many people naturally think there is a high iron content in the water. However, iron measurements with the JBL PROAQUA TEST Fe showed no measurable iron ( 0.02 mg/l). Total hardness (magnesium & calcium) was only measurable in the small Caño Cristalito at 1°. In Caño Cristales both hardness levels were 0! Individual measurements of the magnesium content still showed 1 mg/l. There was no detectable potassium content. Due to the strong current, the many small waterfalls and the paucity of humic substances (clear water), the CO2 content will also have been quite low. Nevertheless, the pH value was 4.5-5. The low conductivity of only 4-5 µS/cm confirms the assumption that only an extremely low amount of minerals can be dissolved in the river water. We wish the biologists working on these plants every success in unravelling the mysteries!
