A pet dog is believed to have killed two sheep and caused six others to drown.
Walkers discovered the dead animals by the Cuckmere meanders at Seven Sisters Country Park, between Seaford and Eastbourne.
Two had their throats ripped out and six had plunged into a nearby waterway.
It is believed the sheep that drowned were unable to escape the water because their wool became waterlogged.
The walkers reported the find to park ranger Simon McHugh of the Sussex Downs Conservation Board, which manages the country park. Police have also been informed.
Mr McHugh said: "Sheep worrying is an ongoing problem in the park. We have sheep worrying incidents right throughout the year but most of them do not end with the death of any animals."
Most of the incidents involve walkers who let their pets off the lead in the 700-acre park.
The dogs chase sheep, which suffer broken limbs or miscarriages as they panic and trying to escape. Some die of shock.
Anyone with information can call Sussex Downs Conservation Board eastern area office on 01323 871095, email east@southdowns-aonb.gov.uk or call police on 0845 6070999.
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