Emergency services were called to Ocean Parade in Coffs Harbor at around 6.50am to find the man, aged 22, with stab wounds.
He is believed to have been attacked during an altercation after emerging from the water.
He was taken to hospital in critical condition but could not be saved.
Detective Chief Inspector Guy Flaherty said the man was found in a car park with “significant” stab wounds.
“We believe the person responsible may have gone back from the parking lot, back to the area of the river and the bridge,” Flaherty said.
Flaherty said police were searching the Coffs Beach foreshore and surrounding areas for “possible items” used in the attack.
A witness who was sleeping rough in the area said he saw the surfer driving around 6am.
“I just saw it come in,” he told NBN.
“Then I went back to put on my runners.
“He just looked like he was just sitting against his driver’s door.”
The police are looking for the offender.
Police are appealing for anyone with information to contact Crime Stoppers on 1800 333 000.
