LA MACARENA, Colombia — Ángela Díaz stood on a rock ledge above a creek called Caño Piedras and pointed out an unassuming olive-colored plant growing below. Macarenia clavigera, she said, is the key to the future of this remote region in central Colombia.

When the rains come in May, the rivers will rise and the plant will turn a brilliant red. “This plant has the peculiar quality of turning distinct colors,” she said. “You can see it from May to November.”

Clear waters alive with scarlet M. clavigera, flowing over the brown rocks of the Guiana Shield, create a brightly colored spectacle each year. Caño Cristales, a nearby river, has become a major tourist attraction, called “the river of five colors” or “the melted rainbow.”

A few paces away, Ms. Díaz, who works as a guide during the tourist season, also noted a tarry seep staining the river rock. This is the other reason this region is getting attention: oil.