Later this year the Yangzi will be blocked and diverted at the site of the Three Gorges dam, a giant project that will turn the 600 kilometres below Chongqing into a lake.
They have also been building a dam of hundreds of sand bags around the bomb site to pump water out in preparation for the delicate task of defusing the device.
Groups are demanding the presence of a Brazilian government high-level official at the site to initiate a new round of negotiations respectful of the rights of local people affected by the dam, the NGO said in a press release on Thursday.