State officials are investigating why an invasive species of fish is dying off by the thousands in the Saint Lawrence River and eastern Lake Ontario. Thousands of round gobies have been piling up on the shorelines over the past two weeks.

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The state Department of Environmental Conservation says the agency doesn't yet know what's causing the die-off. Specimen samples have been sent to Cornell University in Ithaca for testing.

The state College of Environmental Science and Forestry's Thousand Islands Biological Station on the Saint Lawrence River is also investigating the fish kill.

Experts suspect the first gobies to reach the Great Lakes hitched a ride in the ballast water of European freighters.

The fish were first seen in Lake Ontario and the Saint Lawrence River in the mid-1990s. They have displaced native species by breeding faster and eating their competition's eggs and young.