Lake Rotoiti Tasman – current water temperature and swimming conditions
This page provides information about the current water temperature at Lake Rotoiti Tasman in Tasman 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 Lake Rotoiti Tasman today is 6°C.
Water Temperature in Lake Rotoiti Tasman: Daily Trends, Historical Records, and Forecast
❌ Lake water below 10°C is extremely cold and generally unsuitable for swimming for most people. Even during warm weather, deep lakes retain cold water, making entry uncomfortable and limiting time in the water. Swimming at this temperature is usually limited to quick dips or cold-water enthusiasts. Cool air temperatures or cloudy conditions can make lake swimming particularly harsh.
Water Temperature Over the Last 30 Days
Water temperatures in Lake Rotoiti Tasman 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 Rotoiti Tasman will be 6.2°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 | 10.3°C | 6.2°C | |
| Aug 20 | 10.3°C | 6.2°C | |
| Aug 21 | 10.3°C | 6.2°C | |
| Aug 22 | 10.7°C | 6.2°C | |
| Aug 23 | 11.0°C | 6.2°C | |
| Aug 24 | 11.0°C | 6.2°C | |
| Aug 25 | 6.4°C | 6.2°C | |
| Aug 26 | 6.4°C | 6.2°C | |
| Aug 27 | 6.4°C | 6.2°C | 6.4°C |
| Aug 28 | 6.2°C | 6.4°C | |
| Aug 29 | 6.2°C | 6.4°C | |
| Aug 30 | 6.2°C | 6.3°C | |
| Aug 31 | 6.2°C | 6.3°C | |
| Sep 1 | 6.2°C | 6.3°C | |
| Sep 2 | 6.2°C | 6.3°C | |
| Sep 3 | 6.2°C | 6.2°C |
* Current - Actual water temperature value
** Average - Average water temperature on this day in recent years
*** Forecast - Our water temperature forecast
Actual lake water temperatures may differ from the reported values by several degrees, particularly during periods of strong winds or rapid weather changes. Wind can mix surface and deeper layers in a lake, bringing cooler water to the surface, while shallow areas may warm more quickly under direct sunlight. Air temperature, sunshine, and cloud cover strongly influence how quickly a lake heats up or cools down. These factors can lead to noticeable temperature variations across different parts of the lake.
Our forecast is based on a proprietary mathematical model that considers real-time lake temperature observations, historical trends, seasonal cycles, wind strength and direction, and region-specific air temperature. To enhance accuracy, we also incorporate data from nearby monitored locations and comparable lakes within New Zealand.
Monthly Water Temperature Range (Min, Max & Average)
| Month | Today | Yesterday | A Week Ago |
|---|---|---|---|
| January | 6°C | 12°C | 17°C |
| February | 8°C | 12°C | 17°C |
| March | 7°C | 11°C | 14°C |
| April | 4°C | 12°C | 19°C |
| May | 3°C | 7°C | 11°C |
| June | 1°C | 5°C | 9°C |
| July | 0°C | 4°C | 8°C |
| August | 1°C | 5°C | 8°C |
| September | 2°C | 7°C | 11°C |
| October | 3°C | 7°C | 10°C |
| November | 5°C | 9°C | 13°C |
| December | 6°C | 10°C | 14°C |
Lake Rotoiti Tasman: Weather Forecast
August 28
August 29
August 30
August 31
September 1
Location & Local Information
Lake Rotoiti, in the Tasman Region within Nelson Lakes National Park, is a deep alpine lake surrounded by forested mountains and the township of St Arnaud. Fed by cold mountain streams, its water temperature remains low for much of the year. In winter, surface temperatures are generally around 5–8°C. During spring, snowmelt from surrounding peaks keeps the lake brisk, typically between 7 and 11°C. In summer, particularly in January and February, near-shore areas may warm to approximately 12–17°C on calm, sunny days, while deeper water remains significantly colder. By autumn, temperatures usually ease back to between 8 and 13°C. Wind can quickly influence surface conditions on this long, open lake.
Swimming Conditions
Swimming is allowed at accessible shoreline spots, including near the jetty and beaches around St Arnaud. The most comfortable time for a swim is during settled mid to late summer weather when temperatures approach the mid to high teens and winds are light. Even then, the water can feel cold due to its alpine origin, so gradual entry is recommended. Swimmers should choose sheltered bays and avoid windy conditions, as waves can develop quickly. Checking local weather conditions beforehand helps ensure a safer and more enjoyable experience.