At least two days further upriver, the town of SÃO GABRIEL DA CACHOEIRA is the next settlement of any size. Besides the Asabranc service, boats from Barcelos leave at irregular intervals, but generally several times a week; expect to pay between $25 and $35. It’s a beautiful place where the jungle is punctuated by volcanic cones, one with a Christ figure standing high on its flank. Superb views can be had across the valley from the slopes around the town, and there’s a good pensão and several restaurants.

A little further upriver you reach the Rio Negro Forest Reserve, where local guides will take you camping from around $20 a day. At present this park zone – a massive triangle between the headwaters of the Rio Negro and its important tributary the Rio Uaupés, both of which rise in Colombia – is crawling with military personnel. It’s a sensitive zone, partly because of fears of narcotics smuggling, but also because it forms part of the national frontier: Venezuela, Brazil and Colombia meet here, and the Rio Negro itself serves as the border between Venezuela and Colombia for some way. There are also plans to put a highway through the park – the projected BR-210 or Perimetral Norte – which is destined to run from Macapá on the Atlantic coast to São Gabriel, passing south of Boa Vista on the way. From São Gabriel it should eventually make its way across the Amazon via Tabatinga to Cruzeiro do Sul, where it would link up with the westerly point of the Transamazônica, making it feasible to do an enormous circle by road around the Brazilian Amazon. Exactly when this will happen is anybody’s guess (to date only 650km of road near Boa Vista has been built), and some of the regions they are talking about putting this road through are incredibly remote.

You may also be able to get a guide to take you into the Parque Nacional do Pico da Neblina. The Pico da Neblina itself, Brazil’s highest peak at 3014m, is on the far side of the park, hard against the Venezuelan border.

To proceed beyond São Gabriel by river is more difficult, particularly in the dry season from May till October. The river divides a few hours beyond São Gabriel. To the right, heading more or less north, the Rio Negro continues (another day by boat) to the community of Cucui on the Venezuelan border – there’s also a very rough road from São Gabriel. It is just about possible to travel on from here into Venezuela and the Orinoco river system, through the territory of Yanomami Indians. But this involves a major expedition requiring boats, guides and considerable expense: cost aside, it is also potentially dangerous, and you should get a thorough update on the local situation before attempting this route. In recent years the region has become the focus for the garimpeiros who were effectively pushed out of the Yanomami territory in Roraima during the early 1990s and so moved further west into this region, which is clearly one of the last Amazonian frontiers. The left fork is the Rio Uaupés where the Araripirá waterfalls lie a day or two upstream, just before the border settlement of Iaurete. The Uaupés continues, another day’s journey, along the border to the Colombian town of Mitu. Again, this is a potentially hazardous area, home to Maku Indians and, more worryingly, to coca-growing areas and members of the Colombian underworld.