The Tucurui Reservoir in Brazil flooded 1,100 square miles of tropical rain forest, and much of the wood was never logged or recovered.

Decomposing vegetation has resulted in the emission of millions of tons of greenhouse gases. Submerged tree trunks hinder navigation, scientists worry that increasing acidity of water in the reservoir could corrode the dam's turbines, and mosquito infestations have been so intense that some settlements have been forced to relocate.

To solve the problem, until recently, divers using special hydraulic chain saws had been swimming down 70 feet or so into the reservoir, attaching themselves to submerged tree trunks, cutting them and then watching as the trunks were hauled to the surface by iron cables.

"On a good day, you could cut maybe 8 or 10 trees," said Benedito Sidinei Correia de Medeiros, a 38-year-old diver who, after five years, had worked up to a salary of $275 a month. "You have to be very careful down there, because the chain saw can slice you in half if you let it go, and it's so dark during the rainy season that you can't see anything." Also, divers constantly need to be on the lookout for alligators, snakes and a particular species of tree whose bark is poisonous.

http://www.nytimes.com/2004/09/07/internation....html?_r=0