The Marine Research Institute of Iceland estimates that more than 52,000 tons of herring died in the two separate incidents to have occurred in Kolgrafafjörður, West Iceland, over the past two months.
Around 30,000 tons of herring died in December and at least 22,000 earlier this month.
The fishing quota for herring in Iceland for the current fishing season, which runs from September 1, 2012 to August 31, 2013, is 62,234 tons, only 10,000 tons more than the amount of herring which died in the fjord.
According to a statement issued by the Icelandic Food and Veterinary Authority yesterday, the feeding of animals with the dead herring is not legal.
Regulations state that animal fodder should consist of materials which are in a good condition; according to the statement, rotten herring can be harmful.