A fish killed has left 75-hundred menhaden in the Broadkill River dead.
The Delaware Department of Natural Resources and Environmental Control said another 10 Striped Bass and 8 Carp also died.
DNREC suspects low oxygen levels in the river due to heavy rain.
WBOC TV reports that some fisherman in Sussex County said they were worried about their health.
But state officials said there should be no concern yet.
DNREC is testing the water testing.