© APThe Dead Sea: Millions of pounds of herring lie dead, believed to have been killed by building work
Stretching as far as the eye can see, dead herring blanket the ground in these chilling pictures taken today.

It is not yet known what is causing the mass fish deaths in Iceland, but today's grim find is the second such occurrence in two months.

The herring, weighing an estimated 25,000 to 30,000 tonnes and worth £18.9million, were found floating dead in in Kolgrafafjorour, a small fjord on the northern part of Snæfellsnes peninsula, west Iceland, according to the country's Morgunbladid newspaper.

Biologist Róbert Arnar Stefánsson estimates that 7,000 tonnes of herring is laying on the shore and there are many more at the bottom of the fjord.

Both this mass death and the one in December, where a similar amount of fish died, are thought to be due to a lack of oxygen in the fjord caused by a landfill and bridge constructed across the fjord in 2004.

Fears over the costly deaths have prompted the Marine Research Institute of Iceland to visit and gather information, while Government ministers agreed to allocate money to research and monitor the situation.

School children in the nearby village of Grundarfjorour collected between 25 and 30 tonnes of the dead herring this morning for sale as animal fodder.

They raised an estimated £1,000 for use in sports and other activities through the collection.

The herring will be left to decompose naturally, according to a decision by the Environment Agency of Iceland and the West Iceland Centre of Natural History.

Nearby residents complained about the smell of the rotten fish and there is an ongoing dispute over the clean-up.

Tens of thousands of birds have been drawn to the site to feed, but there are fears the fish oil from the decaying herring might threaten these birds in the coming weeks and months.

The fishing industry is a major part of Iceland's economy, accounting for approximately half of the country's total exports.