Stewart Island – current water temperature and swimming conditions

This page shows the current water temperature at Stewart Island in Southland Region. You can view recent sea temperature trends on a 30-day chart, check typical monthly water temperature ranges, and compare today’s reading with historical averages for this date. The page also includes a 7-day water temperature forecast, nearby beaches with similar conditions, local weather information, and a summary of swimming conditions to help you assess how suitable the water is for swimming.

Current Sea Water Temperature

13.4°C

Today

13.4°C

Yesterday

13.7°C

A Week Ago

The average sea water temperature today in Stewart Island is about 13°C.

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

❌ Water at this temperature feels cold and is generally suitable only for brief immersion. Swimming without a wetsuit can quickly become uncomfortable, and exposure time is usually short. These conditions are mainly suitable for experienced swimmers or those using proper thermal gear.

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

From April 14 to May 14

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 13.0°C in the next 7 days. See the table below for daily data for the upcoming week.

Table of Daily Sea Temperature Data

Date	Current	Average	Forecast
May 6	13.5°C	13.8°C
May 7	13.5°C	13.5°C
May 8	13.7°C	13.5°C
May 9	13.8°C	13.8°C
May 10	13.7°C	13.8°C
May 11	13.7°C	13.5°C
May 12	13.6°C	13.3°C
May 13	13.4°C	13.3°C
May 14	13.4°C	13.3°C	13.4°C
May 15		13.3°C	13.3°C
May 16		12.8°C	13.3°C
May 17		12.8°C	13.2°C
May 18		12.8°C	13.2°C
May 19		13.0°C	13.1°C
May 20		12.8°C	13.0°C
May 21		13.0°C	13.0°C

* Current - Actual water temperature value

** Average - Average water temperature on this day in recent years

*** Forecast - Our water temperature forecast

Actual near-shore water temperatures in Stewart Island can vary by several degrees from the values shown, particularly after heavy rain, strong southerlies, or prolonged windy conditions. Certain wind patterns can trigger upwelling, where cooler, deeper water is pushed to the surface and replaces the warmer top layer, leading to noticeable short-term changes in water temperature.

Our water temperature forecast is produced using a proprietary mathematical model that combines real-time measurements with long-term historical patterns, local weather conditions, wind strength and direction, and air temperature specific to each coastal region. To improve accuracy, we cross-check data from nearby locations and use multiple sources, including offshore buoys, satellite-based sea surface maps, and observations provided by local authorities.

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.

Monthly Water Temperature Range (Min, Max & Average)

Month	Min	Avg	Max
January	12°C	16°C	18°C
February	13°C	16°C	19°C
March	13°C	15°C	19°C
April	12°C	14°C	18°C
May	11°C	13°C	15°C
June	10°C	12°C	14°C
July	9°C	11°C	13°C
August	9°C	11°C	12°C
September	10°C	12°C	12°C
October	10°C	12°C	14°C
November	10°C	13°C	15°C
December	12°C	14°C	17°C

* Click on a month to view detailed water temperature data.

Stewart Island: Weather Forecast

May 15

5°C / 11°C

scattered clouds: 25-50%

humidity: 83% | wind: 7 kmh

May 16

6°C / 11°C

clear sky

humidity: 81% | wind: 4 kmh

May 17

6°C / 12°C

scattered clouds: 25-50%

humidity: 82% | wind: 7 kmh

May 18

6°C / 10°C

broken clouds: 51-84%

humidity: 81% | wind: 7 kmh

Local Water Conditions and Nearby Spots

Swimming Conditions

Swimming is allowed around Stewart Island, particularly in more sheltered bays near Oban and Paterson Inlet. These areas can offer calmer water compared to fully exposed coastlines, especially on fine summer days with light winds. Even so, the water remains brisk year-round, and most people opt for short swims rather than extended time in the sea. There are no regular lifeguard patrols, and conditions can change quickly depending on tide and weather. Outside the warmer months, thermal gear is strongly recommended. Stewart Island offers clear water and a stunning natural setting, but the southern ocean temperatures mean swimming is best suited to those prepared for cooler conditions.