Three fourths of water systems on Canadian Indian reservations pose a risk to water quality and health, Canada said Thursday, citing the first large-scale study on the subject.

The almost two-year long investigation revealed that 34 percent of water systems on the reservations pose a "moderate risk" to clean drinking water and health, while 39 percent pose a "high risk. In some areas residents must boil their water before drinking it.

The report "is shocking in that it reveals the quality of drinking water in First Nation communities is even worse than anticipated," said the Assembly of First Nations (AFN) National Chief Shawn Atleo.

Canada has around 1.3 million aboriginal residents out of a total population of 34 million. About 500,000 of them live on reservations across the country. The study was conducted for the Minister of Aboriginal Affairs and Northern Development by a private firm.

Water systems with a high risk of contamination are generally located on smaller, more remote reservations.

"This report shows that more needs to be done, especially in areas like capacity and monitoring, and that is why our government will continue to work with First Nations and will bring in legislation to support the creation of enforceable standards," said Minister of Aboriginal Affairs and Northern Development John Duncan.

In 2005, 800 residents on the Kashechewan reserve in northern Ontario were evacuated after the discovery of the E.Coli bacteria in the local water system, a case that became a centerpiece of the issue.