A major river in the Brazilian metropolis of Sao Paulo is suddenly emerald green and clear skies this week turned from blue to grey. In the late afternoon, the sun's rays filtering through the smoky haze exhibit the color of deep orange.

This isn't a fantasy world: environmental threats in recent days have transformed the colors of the city's landscape.

The state's environmental authority attributes the Pinheiros River's new green hue to an algae bloom, the result of severe drought that has significantly lowered water levels. The phenomenon was visible starting Monday and continued Tuesday. Those same days, the city suffered smoke-filled air, which the agency attributed to a hot, dry mass complicating the dispersal of pollutants originating in forested areas with ongoing wildfires.

Brazil is enduring its worst drought since nationwide measurements began over seven decades ago, with 59 percent of the country under stress – an area roughly half the size of the U.S. Major Amazon basin rivers is registering historic lows. Uncontrolled, man-made wildfires - in the Amazon rainforest and other biomes across the country – have ravaged protected areas and spread smoke over a vast expanse, worsening air quality nationwide.

Residents of South America's most populous city are complaining about both the smoke throughout the city and a putrid smell near the river.

For two consecutive days, smoke caused Sao Paulo, a metropolitan area of 21 million people, to breathe the second-most polluted air in the world, according to data gathered by IQAir, a Swiss air technology company.

Sao Paulo state's environmental agency classified Tuesday's air quality in the metropolitan region as very poor, and advised people to avoid strenuous outdoor exercise, stay hydrated, and keep doors and windows closed.

(Cover: An aerial view of algae pollution at the Pinheiros River in Sao Paulo, Brazil, September 9, 2024. /CFP)