A freshwater scientist says it's impossible for New Zealand to maintain its dairying practices and clean up rivers.

The latest report by the Ministry for the Environment and Stats NZ reveals 45 percent of the nation's rivers are too polluted to swim in.

Two thirds of native birds living near rivers are at risk of extinction and 45 percent of lakes are now more polluted than a decade ago.

Victoria University's Mike Joy says freshwater just cannot handle the pressure it's under.

"Dairy farming in most of the country is that pollution event that we allowed to happen full-time."

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