The River Tiete near Sao Paulo in south east Brazil is being deepened in an effort to prevent annual flooding.
Every wet season the river bursts its banks and floods the city suburbs.
Because it is heavily polluted with industrial waste and household sewage this causes both environmental and health risks.
The local authority has now started a three-year river deepening programme. Some 20km of the river bed is being drilled and blasted and then dredged to deepen it by up to 6m.Dredged spoil will be used to raise the river embankments as a further flood defence.
Work is being carried out by contractors Arcoenge and O'Martin Service, working on a section of river near Barueri in north Sao Paulo. Both firms have two barges on the river, each equipped with two drilling rigs fitted with Sandvik rock drilling rods and 76mm bits.
Holes are being drilled at 3m intervals along the riverbed, using guide tubes to ensure they are drilled straight under water.
After 40 holes are finished, frogmen dive down and load them with explosives and the river bed is blasted. Barge mounted and conventional long-reach excavators then remove the spoil from the river.