Stewart Island – current water temperature and swimming conditions

Water Temperature in Stewart Island: Daily Trends, Historical Records, and Forecast

❌ This is very cold water, causing an immediate cold shock response for most people. Swimming is not recommended without a wetsuit, and even with protection, time in the water should be limited. These temperatures are typically suited only to trained or well-prepared swimmers.

It’s important to note that these swimming tips and recommendations apply only in settled weather. When air temperatures drop below 20°C — and sometimes even below 25°C — swimming can feel uncomfortable, even when water temperatures are relatively high.

Water Temperature Over the Last 30 Days

Water temperatures in Stewart Island have been gradually cooling over the past month, with a further drop recorded during the last week.

According to our forecast, Sea water temperature in Stewart Island will be 11.6°C in the next 7 days. See the table below for daily data for the upcoming week.

Table of Daily Sea Temperature Data

Annual Water Temperature Overview by Month

Monthly Water Temp Ranges

30°C

25°C

20°C

15°C

10°c

5°C

0°C

Annual Water Temperature Trend

Stewart Island, sitting south of the South Island across Foveaux Strait, is surrounded by cool southern waters and a largely untouched coastline. Sea temperatures here reflect the island’s high latitude and exposure to open ocean conditions. In winter, from June to August, the water generally ranges between 8–11°C, which feels very cold and is usually only comfortable for hardy swimmers or those wearing full wetsuits. Through spring, temperatures gradually lift to around 10–13°C. Summer, from December to March, brings the mildest conditions, with sea temperatures commonly sitting between 13–16°C during settled spells. Early autumn can still see 12–15°C before cooling again as winter approaches.