The Spanish Government has fined a subsidiary of the Canadian-Swedish metals company Boliden Ltd nearly $45m over a major toxic spill near a nature reserve four years ago.

It is the largest environmental fine ever imposed by Madrid, Spanish national radio said.

The company has the right of appeal against the decision, which came after a Spanish court cleared the company of any criminal responsibility last year.

Millions of cubic metres of toxic sludge containing traces of heavy metals were released when a mining waste reservoir burst its banks in April 1998.

Thousands of fish and birds died as areas along the Guadimar river were devastated.

However makeshift dykes kept the liquid and mud from flowing into the nearby Donana national park.

The huge reserve provides shelter for millions of migratory birds and houses threatened species such as the Iberian lynx and imperial eagle.

The Spanish Government reopened an investigation last year after Boliden-Apirsa was cleared of criminal responsibility.

The sludge did not enter Donana but coated nearby farmland

Correspondents say it is not immediately clear whether the company, which filed for bankruptcy in October 2000, would be in a position to pay.

The authorities announced a $100m clean-up plan funded by the Spanish Government and the European Union after the spill.

The mine owners agreed to pay for the clean-up, but not damages claimed by landowners.