Prosecutors opened an investigation on Wednesday into allegations by Guarani Indians in central Brazil that their main source of water was deliberately poisoned by farmers.

The charges were made on behalf of the local indigenous group by pressure group Survival International, which said the affected stream was used by the Ypo'i community for drinking, bathing and cooking.

The stream is some 500 kilometers (310 miles) from Campo Grande, capital city of Mato Grosso do Sul state.

Prosecutors said in a statement that "if the contamination of the drinking water is confirmed, the perpetrators face up to 15 years in prison."

Brazil's National Indian Foundation also said it was looking into the case.

The Guarani used a cell phone to capture images of the pollution, including video of white foam that churned up for two days along a stretch of waterway, including a section where they have been camping in the Paranhos region.

"The children were swimming when they saw white foam," the Survival International statement said, adding that along a nearby stretch of the waterway they found two emptied containers of unspecified chemicals.

Survival International said the natives are convinced that the water was poisoned as "a deliberate act and not an accident."

"Those responsible for this cruel and perverse final act should be brought to justice," said the group's director Stephen Corry.

"The federal government should encourage local police to conduct a thorough and impartial investigation."

The disputed land belongs to landowner Firmino Escobar, but part of the property has been occupied by the Guarani since 2010. Survival International says the Indians claim the territory as part of their ancestral lands.

At the beginning of the occupation the landlord cut off all access to water, food and medical care, but a court ordered that the natives should be allowed to remain unimpeded on their small plot until the dispute is resolved.