An open oil pit near La Joya de los Sachas, Ecuador.

Residents of Shushufindi, Ecuador, wash in the water of the Santa Fe River. The residents say toxic chemicals have leached into the soil, groundwater and streams.

SHUSHUFINDI, Ecuador — Mention to Anita Ruíz the name of the giant oil company Chevron, and she trembles with rage. At her wooden hut here in the Amazon forest, where oil-project flares illuminate the night sky, she points to a portrait of her youngest son, who died seven years ago of leukemia at age 16.

“We believe the American oilmen created the pollution that killed my son,” said Ms. Ruíz, 58, who lives in a clearing where Texaco, the American oil company that Chevron acquired in 2001, once poured oil waste into pits used decades ago for drilling wells.