A stream of toxic mud released by a collapsed dam and flowing down a river in Brazil has reached the Atlantic Ocean amid fears of severe pollution impacts on wildlife.

The toxic waste has traveled down the Rio Doce River for two weeks since the waste pond dam at an iron mine more than 300 miles upstream collapsed two weeks ago.

The toxic mud has been tested and found to contain arsenic, mercury, manganese and chromium at levels above what is safe for humans to be exposed to, officials said.

Now that it has reached the Atlantic Ocean, scientists are expressing concern about its possible pollution effects on sensitive marine habitats and the breeding grounds of threatened species including the leatherback turtle, whales and dolphins.

The greatest concern is for the turtles, since the beaches around the river's mouth are the only regular nesting grounds for the leatherback in Brazil.

"If the mud ends up on the beach, this could have a devastating effect on the population," says biologist Antonio de Padua Almeida, head of the local Comboios nature reserve.

Other experts agreed that the potential harm could be widespread and long-lasting.

"The flow of nutrients in the whole food chain in a third of the south-eastern region of Brazil and half of the Southern Atlantic will be compromised for a minimum of a 100 years," said Andres Ruchi, director of the Marine Biology school at Santa Cruz in Brazil's Espirito Santo state.

Samarco, the company that owns the mine where the collapse occurred, has built barriers along the river course in an attempt to protect plants and animals there.

The mouth of the river is also being dredged in an effort to speed up the flow of the toxic mud into the ocean so it can be diluted quickly.

"The best thing that can happen now is for the mud to flow out to sea as quickly as possible," Almeida says. "The mud will have much greater impact on the river than on the sea."

That impact has led Brazil's environment minister, Izabella Teixeira, to describe the incident as "the worst environmental disaster in Brazil's history."

The collapse of the dam on Nov. 5 killed 11 people, and a further 12 are still missing.