Toxic mud that spewed from a mine site when a dam in south-west Brazil burst two weeks ago has reached the Atlantic Ocean.

The collapse of the dam, part-owned by BHP Billiton, buried villages in the state of Minas Gerais, killing at least 12 people and leaving 280,000 without water. Twelve people are still missing.

A plume of mud and mining waste travelled down the Rio Doce from the site of the iron ore mine over the past two weeks and reached the Atlantic Ocean on Monday.

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According to Brazil’s environment ministry, it was expected to spread along a 9km stretch of coastline and past the Comboios nature reserve, a nesting site for the endangered leatherback turtle.

Much of the aquatic life along a 500km stretch of Rio Doce perished since the dam collapse, and the country’s water agency, the ANA, warned of toxic levels of arsenic, zinc, copper and mercury made the water untreatable for human consumption.

It left residents reliant on bottle water.

The dam was operated by Samarco, a joint venture between mining giants BHP Billiton and Brazil-owned Vale.

The mine consortium has laid nine kilometres of floating barriers to try to protect plants and animals from the mud, which is full of heavy metals.

Diggers also worked to widen the mouth of the river to ensure the mud drifted out to sea and disperse as soon as possible.

Well-known Brazilian documentary photographer Sebastiao Salgado, whose foundation has been active in efforts to protect the Rio Doce, described the waterway as a “sterile canal filled with mud”.

Brazil’s president Dilma Rousseff has said the government held all three mining firms responsible for the disaster.

Samarco was already hit with damages, fines and frozen funds totalling more than $400 million.

The clean-up could cost more than $1 billion, according to Deutsche Bank.

See photos of the disaster below

A car balances on a building in Bento Rodigues district, which was covered with mud after a dam owned by Vale SA and BHP Billiton Ltd burst in Brazil. Photo: AAP

Brazilian firemen rescue a foal which remains next to its mother after a dam burst in the village of Bento Rodrigues in Brazil. Photo: AAP

Rescuers are searching for more survivors at the affected village of Bento Rodrigues, in Mariana, the south-eastern Brazilian state of Minas Gerais. Photo: AAP

A fireman rescues a dog that was trapped in the mud that swept through the village of Bento Rodrigues in Brazil. Photo: AAP

– with ABC