Lake Sumner – current water temperature and swimming conditions
This page provides information about the current water temperature at Lake Sumner in Canterbury Region. Here you can view recent temperature trends on a 30-day chart, check typical monthly water temperature ranges, and compare today’s reading with historical averages for this date. A 7-day water temperature forecast, local weather conditions, and an overview of swimming suitability are also included.
Current Water Temperature
The water temperature in Hurunui River at Lake Sumner today is 6°C.
Water Temperature in Hurunui River at Lake Sumner: Daily Trends, Historical Records, and Forecast
❌ River water below 10°C is very cold and generally unsuitable for swimming for most people. Even on a warm day, rivers at this temperature can quickly cause cold shock and numbness due to flowing water and shaded banks. Swimming is usually limited to brief cold dips or experienced cold-water swimmers. Overcast weather or cool air temperatures make river swimming especially uncomfortable and potentially unsafe.
Water Temperature Over the Last 30 Days
Water temperatures in Lake Sumner have been gradually cooling over the past month, with a further drop recorded during the last week.
According to our forecast, the water temperature in Lake Sumner will be 6.8°C in the next 7 days. See the table below for daily data for the upcoming week.
Table of Daily Water Temperature Data
| Date | Current | Average | Forecast |
|---|---|---|---|
| Aug 19 | 10.8°C | 7.2°C | |
| Aug 20 | 10.8°C | 7.2°C | |
| Aug 21 | 10.8°C | 7.2°C | |
| Aug 22 | 11.0°C | 7.2°C | |
| Aug 23 | 11.3°C | 7.2°C | |
| Aug 24 | 11.3°C | 7.2°C | |
| Aug 25 | 5.9°C | 7.2°C | |
| Aug 26 | 6.2°C | 7.2°C | |
| Aug 27 | 5.9°C | 7.2°C | 5.9°C |
| Aug 28 | 7.2°C | 6.0°C | |
| Aug 29 | 7.2°C | 6.2°C | |
| Aug 30 | 7.2°C | 6.3°C | |
| Aug 31 | 7.2°C | 6.4°C | |
| Sep 1 | 7.2°C | 6.5°C | |
| Sep 2 | 7.2°C | 6.7°C | |
| Sep 3 | 7.2°C | 6.8°C |
* Current - Actual water temperature value
** Average - Average water temperature on this day in recent years
*** Forecast - Our water temperature forecast
Actual river water temperatures may vary by several degrees from the reported values, particularly after heavy rainfall or periods of changing weather. Rainfall, river flow rates, and runoff from cooler upstream areas can significantly affect water temperature, especially in flowing sections and shaded stretches. Air temperature and cloud cover also play an important role, with warm, sunny conditions helping rivers warm up more quickly. As a result, noticeable temperature differences can occur along the same river.
Our forecast is based on a proprietary mathematical model that takes into account real-time river temperature changes, historical data, seasonal patterns, river flow conditions, recent rainfall, and local air temperature. We also factor in broader weather conditions specific to each region of New Zealand to improve accuracy.
Monthly Water Temperature Range (Min, Max & Average)
| Month | Today | Yesterday | A Week Ago |
|---|---|---|---|
| January | 10°C | 15°C | 20°C |
| February | 10°C | 15°C | 20°C |
| March | 9°C | 13°C | 17°C |
| April | 6°C | 11°C | 15°C |
| May | 4°C | 9°C | 14°C |
| June | 2°C | 6°C | 10°C |
| July | 2°C | 6°C | 10°C |
| August | 2°C | 6°C | 10°C |
| September | 4°C | 8°C | 11°C |
| October | 5°C | 9°C | 13°C |
| November | 6°C | 11°C | 15°C |
| December | 9°C | 13°C | 17°C |
Lake Sumner: Weather Forecast
August 28
August 29
August 30
August 31
September 1
Location & Local Information
Lake Sumner, located in the Canterbury high country, is closely connected to the upper Hurunui River, which flows out of the lake and continues east towards the coast. The water temperature in this alpine environment remains cool for much of the year due to elevation and snow-fed inflows. In winter, temperatures in the lake and the nearby Hurunui River are typically around 4–8°C. During spring, snowmelt keeps conditions brisk, generally between 6 and 11°C. In summer, on warm and settled days, the lake surface and slower river sections may warm to around 14–18°C, occasionally a little higher in sheltered bays. By autumn, temperatures usually drop back to roughly 8–14°C as air temperatures decline.
Swimming Conditions
Swimming is allowed at Lake Sumner and in suitable sections of the upper Hurunui River, and it can be an enjoyable activity in mid to late summer when water temperatures reach the mid to high teens. However, even in summer the water often feels cold, particularly in flowing river sections where currents are stronger. Swimmers should take care around deeper areas and avoid entering the river during high flows after rain. Choosing calm lake edges or quiet river pools provides safer conditions. As with many alpine locations in New Zealand, checking weather, river levels and local guidance before swimming is recommended.