A girl wading through mountains of trash; a boy up to his neck in toxic waters—these photos show just some of the children exposed to potentially fatal environmental conditions.

At least one in four deaths of children under five, almost 1.7 million children, can be attributed to pollution, according to a newly released report from the World Health Organization (WHO).

A lack of access to potable drinking water leaves children vulnerable to preventable diseases such as diarrhea, malaria, and pneumonia. About 570,000 children also suffer from exposure to air pollutants and indoor pollution, from such causes as cigarette smoke and cooking fires, leading to a greater likelihood they will develop chronic respiratory diseases later in life.

Developing nations are most at