Several tonnes of dead fish have been removed so far from the Siret river, a tributary of the Danube.

The accident comes almost exactly a year after another cyanide spill in north-west Romania which devastated river life in three countries.

The latest accident appears to have been caused by workers deliberately emptying cyanide solution from tanks at a bankrupt detergent factory into the Siret.

One man has been arrested and the company fined the equivalent of $800.

Mines threat

In the meantime, the cyanide has been making its way down the Siret, a major river in eastern Romania, towards the Danube delta and the Black Sea.

The previous spill drew mass protests

Almost a year ago, 130,000 cubic metres of cyanide-tainted water leaked from a gold mine at Baia Mare in north-west Romania.

A European Union report on the accident published at the end of last year blamed design faults at the mine alongside other factors.

The Romanian authorities have identified some 40 mines and factories which pose a serious threat to the environment and have appealed for international help to install safer technology.