A bloody shark's head has been found impaled on the fence of a Marine Rescue NSW base.

The volunteer-run organisation posted the grisly images online showing the fish head, believed to be that of a mako shark, spiked on the fence of their Shellharbour base on Saturday morning.

"It's a kick in the guts for our committed volunteers who give up their time to save lives on the water," the organisation wrote on Facebook on Monday.

The shark's head appears to have cigarette butts and debris packed into its mouth.

Volunteers and residents reacted with shock and disgust.

"As a Marine member myself this is terribly disrespectful," one said.

"Someone with a macabre sense of humour," another added.