Cottesloe Beach Water Temperature & Swim Forecast

The sea in Cottesloe Beach peaks in February, when the water averages around 23°C.

The main swimming season runs from October – May, when surface temperatures stay comfortable for extended sessions.

On average, 8 months a year sit above 20°C — the threshold most swimmers describe as pleasant without a wetsuit.

Shoulder months like September and June are noticeably cooler but often quieter, with fewer crowds and steadier weather.

The coldest month is typically July at around 18°C, when cold-water swimmers dominate the coast.

Cottesloe Beach sits in the Southern Hemisphere, so the warmest sea coincides with the December–February summer and the coolest with July–August.

Long-term climatology for Cottesloe Beach shows an annual mean sea temperature of 20°C, ranging from 18°C in winter to 23°C at the summer peak.

The seasonal swing is roughly 5°C between the coldest and warmest month — a useful yardstick when comparing years or checking whether the current sea is running above or below average.

Recent decades have trended slightly warmer at Cottesloe Beach, in line with regional sea-surface temperature records for the wider basin.

Monthly averages below are drawn from multi-decadal climatology and are updated as new observations arrive.