By Adam Easton
BBC News, Warsaw
Polish Prime Minister Jaroslaw Kaczynski has said planned work on a road through one of Europe's last remaining wetlands will not go ahead.
Lynx, wolves and rare warblers live in the valley (Picture: P Malczewski)
Earlier, Poland said construction work on a bypass through the environmentally protected Rospuda river valley would start on Wednesday.
But the prime minister changed his mind after the EU applied for an immediate injunction to stop the work.
The valley is home to rare plants as well as wolves and eagles.
Speaking on Polish public radio, Mr Kaczynski said his government had failed to convince the European Commission and it was now time to show a certain restraint.
The valley is also protected under the EU's Natura 2000 conservation scheme.
The government wants to build an elevated highway right through the valley to ease traffic in the nearby town of Augustow.
The town lies on the main route from Poland to the Baltic states and thousands of heavy goods lorries pass through it every day.
Hundreds of people from the town spent the whole night blocking the road in a peaceful protest.
They want the bypass built as quickly as possible, even if that means routing it through the valley.
Until now, the government has argued that an alternative route suggested by environmental conservation groups would take too long to build.