Berlin - Environmentalists plan to continue their resistance to a mega-bridge crossing the strait between Denmark and Germany despite the signing of a treaty to forge ahead with the project, a nature-protection group, NABU, said Wednesday.

They fear migrating birds will thud into the towers of the 19- kilometre suspension bridge while the piers will slow the flow of water through the Fehmarn Belt into the Baltic Sea.

Replacing car ferries that depart half-hourly round the clock will take about an hour off the 4.5-hour, straight-line motorway drive from the Danish capital Copenhagen to the German city of Hamburg.

German and Danish ministers were set to sign a treaty in Copenhagen Wednesday authorizing the bridge between the little Danish port of Rodby and the German island of Fehmarn.

"We'll obstruct the project in the courts any way we can," said NABU's national secretary, Leif Miller, in remarks quoted by the Berlin newspaper Tagesspiegel.

The project closes one of the last bridgeable gaps in the landmass occupied by the European Union and will also benefit Sweden, which is already connected to Denmark by the Oresund mega-bridge. Fixed links already exist, but involve a detour via the Jutland peninsula.

The signatures were to be placed on the agreement by German Transport Minister Wolfgang Tiefensee and his Danish counterpart Carina Christensen.

The project forms part of a larger infrastructure project which the Danish parliament agreed Tuesday. Total costs are estimated at 5.6 billion euros (8.1 billion dollars). The Danish government is to contribute 4.8 billion euros.

The costs will be recouped by introducing a toll. Work is scheduled to start in 2011 and be completed by 2018. (dpa)