Several species of marine turtle bury their eggs at the mouth of the Paraiba do Sul river where the spill has spread over more than 50 square kilometers (19 square miles) off Rio de Janeiro state, the environment secretariat said.

The substance, which includes caustic soda, is slowly headed north towards the beaches of Espiritu Santo state.

A biologist working to protect the turtles warned of "tragedy" if the spill reaches the wetlands in the area.

"The destruction of these wetlands would be a big tragedy because they are a sort of 'maternity ward' for various species of sea turtle," he said.

Some 20 million liters (5.3 million gallons) of the toxic waste escaped a week ago from a paper factory in Minas Gerais state, contaminating the Pomba river. The Pomba flows into the Paraiba do Sul river, through the neighboring state of Rio de Janeiro and out to sea.

Several towns along the coast, many of which are expecting a crowd of tourists for the Easter holiday, were concerned that beaches were covered with a thick, bad-smelling foam on Saturday.

Environmental official Flavio Montiel said after flying over the region in a helicopter that the spill had reached the sea and was following the wind and sea currents.

Alberto Dauaire, mayor of Sao Joao da Barra, said fishermen were having problems with their boats.

"These substances are toxic and corrosive. Besides killing fish and livestock, they are causing damage to the motors of fishing boats," he said.

The paper factory was shut down and ordered to pay an initial 50-million-real (15 million dollars) fine.

SPACE.WIRE