New Zealand's strong economic growth is placing strains on the environment that threaten to undermine its "clean, green" reputation, the Organisation for Economic Co-operation and Development (OECD) warned Tuesday.

The South Pacific nation has long marketed itself internationally as "100 percent pure" and is undergoing a tourism boom as visitors flock to see the spectacular scenery featured in films such as "The Hobbit" trilogy.

But an OECD report said the environment was paying the price for growth in the farm-reliant economy, which is currently among the strongest in the developed world at more than 3.0 percent.

It said intensive dairy farming had left many rivers with elevated nitrogen levels, making them vulnerable to algal blooms.

The report, the result of a once-in-a-decade review, also noted that New Zealand had one of the worst rates of species extinction in the world.

In addition, per capita greenhouse gas emissions were the fifth highest in the OECD and rising, while emissions in most other countries were on the decline.

The report said government plans to double agricultural exports by 2025 were set to worsen the problems.

"New Zealand's growth model has begun to show its environmental limits, with increased greenhouse gas emissions and waste generation, freshwater contamination and threats to biodiversity," the report said.

"This may indicate that New Zealand's strong growth has come partly at the expense of environmental quality, a dynamic that puts the country's 'green' reputation at risk."

It recommended Wellington strengthen its emission trading scheme and expand it to agriculture, which is currently exempted even though it accounts for half of the country's emissions.

Environment Minister Nick Smith welcomed the report and said the government was already working on many of the issues it raised.

"This environmental report card will help us sharpen our future direction and environmental aspirations, as well as learn from the experiences of other countries," he said.