With Sydney tipped for a scorcher this weekend, police are urging common sense at the beach.
In NSW, the Bureau of Meteorology is forecasting temperatures to reach more than 10C above average in some parts of the state over coming days.
In Penrith and suburbs in Sydney's west, a maximum of 41C is forecast for Friday.
The mercury reached 30C about 10am (AEDT).
Police have reminded people people not to leave children and animals in cars even for a few minutes during the hot spell.
And police acting inspector Alex Barrell urges people to assess the conditions before swimming, whether at the beach, in a river or a pool.
"The appearance of many waterways can be deceiving, whether it is depth, current, temperature or submerged objects, so it's important to check before you get in," he said.
At NSW beaches, more than 21,000 surf lifesavers will watch over swimmers.
Beachgoers who don't swim between the red and yellow flags put themselves at risk.
Surf Life Saving NSW lifesaving manager Andy Kent urged people to swim at patrolled beaches.
In 2012/13, the NSW coastal drowning toll was 48, the highest in many years, he said.
The high temperatures mark the first heatwave of the summer and it will linger in the state's northeast into early next week, the bureau says.
A total fire ban has been issued for the southern Riverina, northern Riverina, Illawarra/Shoalhaven and eastern Riverina on Friday.
