By Paulo Cabral
BBC Brazilian Service
The virtual disappearance of a waterfall at Brazil's Paulo Afonso gorge - once called "Brazil's Niagara" by Victorian explorer Richard Burton - is perhaps the most visible of a number of changes along the Sao Francisco river made in order to generate hydroelectric power.
Where Richard Burton saw the Brazilian Niagara, today there are only rocks
"The Paulo Afonso gorge is filled with what seems not water, but the froth of milk - a dashing and dazzling, whirling and surfaceless mass, which gives a wondrous study of fluid in motion," Burton wrote when visiting the country in 1867.
But this magnificent waterfall has been reduced to a mere trickle in recent times after the course of the Sao Francisco river that flows through the gorge was altered by the building of a huge dam.
Some 40% of the power used in north-east Brazil now comes from the Paulo Afonso hydropower plant - like many in the country, the source of much controversy since its construction.
But this has come at a cost to both people and the environment, reflected in the loss of the Paulo Afonso waterfall, once the biggest attraction in the whole region.
Edson Pires, one of the main managers of the electric system in the region, admitted that the building of the dam had had some negative consequences.
"Many people were displaced, and many cities were flooded when the dams were built to provide water for these power plants that are on the Sao Francisco river," he conceded.
But he added that steps had been taken wherever possible to minimise the impact.
The Paulo Afonso power plant is essential to provide electricity to the Brazilian north-east
"These people were rehoused in villages that were built along the Sao Francisco river, with irrigation projects and new houses," he said.
"I guarantee that nobody is without a house because of a lake."
Mr Pires said that he personally felt strongly about any environmental impact the dam may have had.
"This is a rare kind of river. It's beautiful, the quality of its water is really high and I feel really happy when I occasionally swim in its water," he insisted.
"This is something very important for me."
Many of those who work in the industry take a similar view, and sing the praises of both the river and the power plant - there is even a corporate CD of such songs.
Some add that the Paulo Afonso waterfall may not be gone forever.
According to Antonio Gaudino of the Sao Francisco Power Company, its waters can be unleashed again at the flick of a switch.
"It is a programmed waterfall - if the dam opens its floodgates, the Paulo Afonso waterfall will return," Mr Gaudino explained.
He added that he felt the changes made to the river to accommodate the dam only added to the region's appeal to tourists.
"There is adventure here - there are several canyons that could provide for bungee jumping or other activities like this," he said.
Animal trafficking is a major focus for the Brazilian Environmental Police
"After the dam of Xingo - about 60 km down the river from Paulo Afonso - the canyons of the Sao Fransisco started to be navigated.
"Before there were rapids here. Now the level of the river is a bit higher - because of the engineering works - it's possible to have different kinds of boats going down the river."
But the loss of the Sao Franscisco's powerful flow has had other environmental costs.
In 1867, the Paulo Afonso marked the end of Burton's journey, as the rapids beyond would have capsized his canoe - today he would be able to follow the Sao Francisco all the way to the Atlantic.
In the past, water from the river could be found as far as seven km into the Atlantic Ocean.
But the reduction in flow means now it is the sea that can be found about two km inland - causing erosion and damage to the beautiful mouth of the river.
Slightly further inland at the town of Pinanhas, Brazil's environmental police are fighting another battle.
The area is suffering from the impact of the illegal trade in wild animals and birds, the police's Sergeant Marcelo Jose da Silva said.
Animal smugglers have been using traps with the appearance of a First Aid Kit
He outlined the vast number of ways in which animals are transported and hidden from the police.
One is a box with "pharmacy" on the label - suggesting it contains First Aid equipment - but it actually contains traps in which birds are hidden, in terrible condition.
Another method is a plastic water pipe - again, used to keep birds inside.
The commitment of the battalion to the wildlife is obvious.
"It's very rewarding to be working with wildlife and nature in Brazil, but at the same time it's very shocking to see some of these things," said Private Altair Siqueira, with the group since it was established in 1988.
"To see people destroy nature and kill animals for pure pleasure makes me cry sometimes.
"I'm moved even I talk about that."
He added that he felt it was "beautiful" when traders were caught.
"We can just break the cages, give food, give water to these birds - and then we can release these birds back into the wild," he said.
"The birds just fly around over the heads of the policemen in a sign of thanks."
It is surely to be hoped that their work continues to be successful, before the birds and animals go the same way as the Paulo Afonso waterfall - to be found only in the books of the past.
Paulo Cabral travelled to north-eastern Brazil for the BBC, keeping an online journal along the way. His three-part series, Blogging in Brazil, concludes on BBC World Service, on 20 August.