By Mexico correspondent Peter Greste

Greenpeace and at least 50 Mexican environmental groups have filed a criminal complaint against the world's biggest open-air salt evaporation plant for the deaths of almost 100 turtles in a wildlife reserve.

The complaint blames pollution from the salt works on Mexico's Baja California peninsula for the deaths of the protected sea turtles and other marine life.

The legal action is being taken by campaigners to stop the salt company - a joint consortium run by the Mexican Government and the Japanese Mutsubishi corporation - from opening a second plant.

For months gray whales, dozens of sea turtles and hundreds of fish have been found dead along the spectacular coast of Mexico's Baja California peninsula.

Most have turned up within the Vizcaino Biosphere reserve, the largest sanctuary of its type in Latin America.

Environmentalists investigating the deaths say the open-air salt evaporation plant called Exportadora de Sal SA is to blame for dumping concentrated brine laced with heavy metals into the Ojo de Liebre lagoon.

Breeding ground

The lagoon is a key breeding ground for both sea turtles and endangered gray whales.

In a statement the coalition of environmentalists said that through their inspections the Mexican authorities had concluded that the company caused the turtle deaths.

One of the environmentalists leading the court case said the Mexican Government's shareholding creates a direct conflict of interest.

The government is not only the majority stake-holder in the company, it is also legally responsible for protecting the biosphere.

In a statement the salt company denied it had made any discharges and insisted that its operations are both natural and environmentally friendly.