NEPTUNE - The Monmouth County Health Department says early morning visitors to the the Shark River reported thousands of dead fish washed up on the beach.
Low tide revealed the gruesome sight in the marina, in the shallow river bottom and along the shoreline.
Local fishermen have several theories about what killed the bunker fish, commonly used as bait.
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One told News 12 New Jersey he watched a school of Bluefish feeding on bunker fish and then saw them push all of them into the shallows where they were trapped. Another person says a commercial boat at the inlet pushed them into the shallows.
The DEP is looking into whether or not the fish died of disease or a shortage of oxygen.
Public health coordinator Michael Meddis says bunker reproduce in large numbers and typically use a lot of oxygen.
Many around the arena believe a lack of oxygen could have been prevented if the Shark River had been dredged at some point in the last 12 years. "We have excess sand in this river that needs to come out desperately," says Neptune Committeeman Eric Houghtaling.
The DEP is taking samples of the fish and water for testing.