Caño Cristales

The colour is a plant, and it only works four months a year

Caño Cristales, the Crystal Channel, runs fast and clear over the quartzite of the Serranía de la Macarena, an isolated range in Colombia's Meta Department, on its way to the Guayabero River and the Orinoco. The rock is about 1.2 billion years old, a western outlier of the Guiana Shield, and the bed is pocked with giant's kettles, round pits drilled by harder stones the current spins in place. The water is so clear because it carries almost no nutrients or fine particles.

For most of the year it looks like any other river, dull green moss under a cool current. Then, in the short span between the wet and dry seasons, from about late June or July into November, when the water level is just right, it becomes the river of five colours: yellow, green, blue, black and above all a vivid red. The red is a plant, Rhyncholacis clavigera, long known as Macarenia clavigera, a member of the riverweed family often mistaken for algae. It grips the rock where the current runs fastest, green when young, then yellowish, then every shade of red, and it grows only here and in a few other rivers of the region, such as the Caño Siete Machos. The range sits where the Andes, the Llanos and the Amazon meet, and despite claims to the contrary the river holds fish and freshwater turtles too.

Cattle farmers found Caño Cristales in 1969, but for decades few outsiders could follow them. The FARC held the region; visiting in 2017, after the peace accord, President Juan Manuel Santos recalled that during the war no Colombian could or dared come, because the guerrillas controlled it completely. The river reopened to visitors in 2009, and arrivals in La Macarena climbed from 3,847 in 2012 to 15,907 in 2016.

Getting there is still an expedition. Visitors fly into the little town of La Macarena, which requires a yellow fever vaccination, and go on by boat up the Guayabero and then on foot or horseback, always with a local guide; no one may enter the park alone, stay overnight or cook. Daily numbers are capped, with 172 allowed in the Caño Cristales sector. Sunscreen and insect repellent are banned because they harm the plant, and Cormacarena, the regional authority that manages tourism, gives every group a compulsory briefing and hands out entry wristbands. When the river drops in the dry season, the site closes, and in 2023 Cormacarena warned that anyone slipping in during the closure faced fines of up to 5,000 minimum salaries.