The Shoreham inshore and all weather lifeboats were launched to reports of a person face down in the water at Worthing.
The inshore lifeboat crew started a search of the area and quickly located the woman 50 metres from the shore at Splashpoint.
The crew pulled her aboard and then beached the inshore lifeboat so a crew member could undertake CPR on her ashore.
An ambulance crew was waiting on the beach and took over but sadly pronounced the woman dead.
The all weather lifeboat stood off ready to assist the inshore lifeboat if needed. The inshore lifeboat then relaunched and both boats returned to station.