Just this week in Hampton Bays, New York, thousands and thousands of dead bunker fish filled up the Shinnecock Canal. They had been starved of oxygen.
https://www.youtube.com/watch?v=Gu5LnlLNZcE
The New York State Department of Environmental Conservation believes the fish were fleeing a predatory school of bluefish when they wandered into the canal. However, the canal was a dead end because it was closed for the night. As the numbers of fish grew there was rapid depletion of oxygen in the water and thousands of fish were asphyxiated.
The next morning when the locks opened, many of the dead fish floated back out to sea, or washed up on shore and some even made it out alive.
https://www.youtube.com/watch?v=riwtl_kPe0g
Even though this seems like a open and closed case, the county’s health department is collecting water samples to test for pathogens and pesticides.
Source: Gizmodo