raimundo bacelar says it contains too little oxygen, and that the plants and trees that were cut down weren't removed before the water flooded in. >> when the water rose, it all went very fast. it didn't make the fish sick at the beginning. and it's not that two or three fish died at first- then we could have done something. but no. they all died at once almost immediately. when we arrived, the breeding enclosures were white from the fish floating on the surface. >> they lost more than 80 tonnes of fish, and here, too, nobody knows whats going to happen. most fishermen in the region say the lake has far fewer fish now. the dam operator disputes that, citing various studies that suggest the opposite. philip fearnside, a renowned amazon researcher, thinks the fishermen's assessment is realistic. for years, he's been studying the impact of building dams in tropical climates. >> the lower layer of water in the artificial lake no longer has any oxygen. that means all the roots, leaves and other organic matter decaying there aren't releasing carbon dioxide, because they aren't getting any o