Dee Why Lagoon – current water temperature and swimming conditions
This page provides information about the current water temperature at Dee Why Lagoon in New South Wales. 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 Dee Why Lagoon today is 19°C.
Water Temperature in Dee Why Lagoon: Daily Trends, Historical Records, and Forecast
⚠️ A lake temperature of 15 to 20°C is considered cool to comfortable for swimming in Australia. On warm days with light winds, this range allows for relaxed swimming, especially in shallow or sheltered areas. Comfort depends strongly on air temperature and sunshine, as cooler or overcast weather can still make the water feel chilly. This range is common during spring and early summer.
Water Temperature Over the Last 30 Days
Water temperatures in Dee Why Lagoon 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 Dee Why Lagoon will be 17.9°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 |
|---|---|---|---|
| Apr 8 | 19.2°C | 17.7°C | |
| Apr 9 | 19.2°C | 17.7°C | |
| Apr 10 | 19.2°C | 17.7°C | |
| Apr 11 | 20.0°C | 17.7°C | |
| Apr 12 | 20.0°C | 17.7°C | |
| Apr 13 | 18.5°C | 17.7°C | |
| Apr 14 | 18.5°C | 17.7°C | |
| Apr 15 | 20.0°C | 17.7°C | |
| Apr 16 | 18.9°C | 17.7°C | 18.9°C |
| Apr 17 | 17.7°C | 18.8°C | |
| Apr 18 | 17.7°C | 18.6°C | |
| Apr 19 | 17.7°C | 18.5°C | |
| Apr 20 | 17.7°C | 18.3°C | |
| Apr 21 | 17.7°C | 18.2°C | |
| Apr 22 | 17.7°C | 18.0°C | |
| Apr 23 | 17.7°C | 17.9°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 Australia.
Monthly Water Temperature Range (Min, Max & Average)
| Month | Today | Yesterday | A Week Ago |
|---|---|---|---|
| January | 15°C | 23°C | 26°C |
| February | 20°C | 23°C | 26°C |
| March | 19°C | 21°C | 24°C |
| April | 16°C | 18°C | 20°C |
| May | 11°C | 14°C | 17°C |
| June | 8°C | 11°C | 13°C |
| July | 8°C | 10°C | 13°C |
| August | 8°C | 11°C | 13°C |
| September | 12°C | 14°C | 17°C |
| October | 15°C | 17°C | 19°C |
| November | 18°C | 20°C | 24°C |
| December | 13°C | 23°C | 25°C |
Location & Local Information
Dee Why Lagoon sits just behind the beach on Sydney’s Northern Beaches and is a shallow coastal lagoon influenced by rainfall, runoff, and seasonal weather rather than ocean conditions. Water temperature varies through the year but tends to be moderate. In summer, the lagoon usually warms to around 22–26°C, which can feel quite warm on still days. Spring and autumn typically sit between 18–22°C, while winter temperatures often drop to about 14–17°C. Because the lagoon is shallow, temperatures can change quickly depending on air temperature, sunshine, and recent rain.
Swimming Conditions
Swimming in Dee Why Lagoon is generally not recommended. While water temperatures in summer may appear suitable, water quality is often affected by urban runoff, stormwater inflow, and occasional algal growth, particularly after rain. For this reason, the lagoon is not managed as a designated swimming area, and locals usually avoid swimming there. After heavy rainfall, conditions can deteriorate further, with reduced clarity and increased health risks. As a result, most people choose the nearby ocean pool or beach for swimming instead. Overall, Dee Why Lagoon is best appreciated as a natural wetland and scenic feature rather than a recreational swimming spot, despite having seasonally mild water temperatures.