Pollution is one of the major problems in parts of these river basins. On the Jari River, a single pulp mill discharged over 24,000 tonnes of contaminants containing chlorine, magnesium, potassium, aluminium and iron in one year, causing a major die-off of the fish on which the dolphin feeds in the river.
Another major problem is the 2,000 tonnes of mercury released into the forests and rivers of the Brazilian Amazon by gold miners, who use it as part of a primitive technique to purify the gold. Fish in the Maderia, an Amazon tributary, now contain five times the permitted methyl-mercury levels and these poisons are concentrated as they pass up the food chain to the dolphins and humans.
The Brazilian government has ambitious plans to build more than 60 dams for hydro-electric power in the Amazonian region by the year 2010,although only seven are currently completed and in operation. The damming of one river in the State of Para in Brazil, led to the loss of 17 out of the 22 fish species found there; only two of the remaining five left are still abundant. The botos' general feeding pattern includes 50 species of fish; having their diet reduced to only two species might prove fatal.