John Boorman's
The Emerald Forest
(1985)

Bill Markham (Powers Boothe) is an American engineer working on a project to build a dam in the Amazon rain forest. His family comes out to visit him in this remote location. His small son Tommy is kidnapped by members of a small tribe. This tribe is referred to as the Invisible People. They disappear deep into the rain forest with Tommy. Bill spends the next 10 years searching for Tommy. He travels through the vast undeveloped jungle, and visits various primitive tribes.

After 10 years, Bill finds the invisible people with Tommy. Tommy is now about 17 years old. Bill stays long enough to learn some of their language and develop a relationship with Tommy. Tommy considers himself one of the invisible people and refuses to return home with Bill. Shortly after Bill leaves, a raiding party of another tribe captures the women of the invisible people. The women are sold to a brothel at the dam construction site. The invisible people try to rescue the women, but they are no match for the guns of the guards at the brothel. Desperate, and with no other options, Tommy travels to the city to seek his father's help. Bill supplies guns to the tribe, and helps them liberate the women.

Bill tries to explain to Tommy and the rest of the tribe that the dam is almost complete, and it will completely disrupt their lives. In addition to flooding their land, the hydroelectric dam will lead to greater development in the area. The Invisible People can not believe his description of what will happen, and will not flee deeper into the rain forest. Bill realizes that the way of life his son has chosen will be lost forever. Bill is still an engineer on the project. He enters the dam and places explosives that destroy the dam.

Thanks Joseph C!