In Brazil, most rivers, lakes and reservoirs have bad or very bad water quality near metropolitan areas, a report released Tuesday by the National Water Agency (ANA) said.

The water quality index indicated the country's aquatic system is heavily polluted in the vicinity of metropolitan areas such as Sao Paulo, Curitiba and other medium-sized cities, according to the report "Water Situation in Brazil in 2011." The report is based on data collected in 2009.

"This condition is mainly associated with domestic sewage spills," the report said.

According to the report, between 2005 and 2009, there was an increase in investment related to wastewater treatment, especially through the so-called PAC sanitation projects (the government's Program to Accelerate Growth).

Sanitation policies have been effective in improving water quality, but large investments are still needed in the future, Environment Minister Izabella Teixeira said while presenting the report.

She pointed out that 69 percent of the country's water resources are used for irrigation, and more than 90 percent of that amount goes to the private sector. The government has to see whether the irrigation areas have an adequate water supply to ensure agricultural production.