Reflooding of Iraq's destroyed Mesopotamian marshes has resulted in a "remarkable rate of reestablishment" of native invertebrates, plants, fish and birds, says a team writing in the journal BioScience.

The research group, from Duke University in the US and Iraq's University of Basrah, say that water inflow from the Tigris and Euphrates rivers has been greater than expected because of record snowpack melts, which has kept salinity levels low.

The incoming water quality has also been better than predicted, with toxin levels lower than had been feared.

As a result, many native species have returned, including some rare bird species, although their numbers have not rebounded to historical levels, according to the team.

The wetlands were drained during the 1980s and 1990s as punishment after the Marsh Arabs gave sanctuary to rebels fighting the Saddam Hussein regime.

This lead to tens of thousands of marsh Arabs fleeing to southern Iran.

It is estimated that during the Saddam period, around 95 per cent of the marshes dried out.

Duke University scientists made their first assessment of the status of the marshes in June 2003.

They discovered that local farmers began to blow up dikes and dams after the collapse of the Hussein regime in April 2003.

Subsequent monitoring, done in collaboration with scientists from the University of Basrah, estimated overall ecosystem health.

The team report that 39 per cent of the former extent of the marshes had been reflooded by September 2005.

Despite incomplete data, the researchers found that in many respects the restored marshes they studied are functioning at levels close to those in one marsh that remained undrained.

The fast recovery of plant production, overall good water quality and rapid restoration of most wetland functions seem to indicate that the recovery of ecosystem function is well under way.

But the researchers point out that water inflow is unlikely to be sufficient to maintain the encouraging trends in coming years.

Fish catches remain poor, which deters many Marsh Arabs from returning to a traditional way of life.

Further research is needed, say the researchers, to determine how the marshes and agriculture can share water, to identify sites of toxins, and to study insecticide use by local fishermen.