The woman may have entered the water to hekp her son who was caught in a rip but got into difficulty herself, Surf Life Saving NSW said.
Surf Life Saving officers at the scene said the surf conditions were quite large at the beach, with a 1.5 metre swell and large sets of waves.
Congo Beach is not patrolled by lifesavers.
Steven Pearce, chief of Surf Life Saving NSW, told people to take precautions such as taking a floatation device when attempting to rescue someone.
“It is a natural reaction to race into the water when we see our family and friends get into difficulty, but we’re pleading with people to stop and think for a moment before diving in and to look for a nearby rescue device, or even an Esky lid or bodyboard, to use as a flotation device,” Mr Pearce said.
“It can make a huge difference to the outcome.”
The boy was assessed by paramedics but was not injured.
Police have begun an investigation and a report will be prepared for the coroner.
