Published: 2018-11-21 20:29:26 BdST
Thousands of tonnes of freshwater carp have washed up dead this month, leaving Iraqi fish farmers reeling from the significant loss of earnings.
Carp is the country's national dish, commonly served barbecued.
Agriculture officials had ruled out deliberate poisoning. A joint investigation by the Iraqi health ministry and WHO also revealed the contamination was not toxic to humans.
"Testing on dead fish has revealed serious issues that warranted WHO to conduct a second investigation related to probable viral infection of fish causing the death of thousands in the river. Results of the second test are due next week," WHO said in a statement on Tuesday.
The incident illustrates worsening pollution problems in Iraq, which is struggling to provide a sufficient supply of clean water, especially in the south of the country.