A massive school of herring has washed ashore on a beach in Norway where some witnesses’ estimates had placed the number of dead fish in the tens of thousands.

Local media reported that some 20 tons of fish were found at the end of December on a beach in northern Norway.

The fish appeared on New Year's Eve, leading to speculation that predators might have driven a huge school ashore or the fish could have been washed onto the beach by a powerful storm that hit Norway on Christmas Day.

"We have seen herring stranded before but never this much," Ole Kristian Berg, biologist at the Norwegian University of Science and Technology in Trondheim, told AFP.

Berg went on to explain the herring may have been chased up on land by other fish or other ocean predators. They may also have fallen victim to the tides or high levels of freshwater in the area, where a river flows into the ocean, he said.

Jens Christian Holst of Norway's Institute of Marine Research believed a combination of several factors was the likely explanation.

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Locals also started pondering how to clean up the estimated 20 tons of dead fish on the beach in Kvaenes, near Tromsoe, north of the Arctic Circle, before it decayed, according to The Vancouver Sun.

According to the Nordreisa municipality, before they could start with the cleanup, most of the fish disappeared due to the tides and have now been swept out into the North Sea by the tides.

Herring are found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. The trade in herring is an important sector of many national economies.

In Europe herring has been called the "silver of the sea", and its trade has been so significant that it has been regarded as the most commercially important fish in history.