With hot sunny weather expected across much of the country, millions of people are expected to cool off with a dip during the next four days.

Nationally, there have 51 drowning deaths so far this summer. By January 25, last year 77 people had drowned.

In NSW since December 1, there have been 13 coastal drownings. Three of those occurred during the past 48 hours.

"All of these drownings have been in unpatrolled locations," Surf Life Saving NSW chief executive officer Steven Pearce said.

"There has not been a drowning within the red and yellow flags or at a patrolled location."

It's a common misconception that drownings mainly occur at the beach.

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"There have been three times more drownings at inland waters this year to date in Victoria," Life Saving Victoria said.

"It's important to remember that rescue is the last line of defence against drowning, and we'd rather these services weren't needed at all. Prevention is better than rescue."

Surf Life Saving Queensland urged people to look out for their friends and family while swimming.

"If someone has been drinking, going for a swim isn't safe," the rescue group said.

"A 'she'll be right' attitude won't save your life this summer."

NSW Minister for emergency services Steph Cook urged parents and carers to keep a close watch on their children when near water.

"They can shoot off really quickly and before you know it you've lost sight of them, and that can result in tragedy," she said.

Mr Pearce urged anyone heading to the coast to only swim at a patrolled location.

"Anywhere that you see lifeguards or lifesavers on duty, anywhere you see those red and yellow flats," he said.

Lifesavers will be patrolling from the beach, the water and the air.