Fallout from Brumadinho dam collapse harming crucial Brazilian river

A fear shared by hydrologists, environmental activists, and millions of northeastern Brazilians has come to pass. The report “Water Quality in Brazil’s Atlantic Forest,” by the SOS Mata Atântica Foundation, concludes that the mud spilled from the Brumadinho dam collapse in January has now reached the São Francisco river—the longest waterway to run entirely within Brazil’s borders. The news is all the more worrisome as the river is responsible for 70 percent of available fresh water in the Northeast—the aridest region in the country.

Between March 8 and 14, the NGO collected water samples from the Paraopeba river—which was directly affected by the January 25 dam spill—and from the São Francisco, including the Três Marias Dam, which holds a 21-billion-cubic-meter reservoir.

“The mud from [mining company] Vale is visible until the middle of the lake. But even where the greenish color of...