Water temperature

Water temperature is one of the things that affects fishing the most. Fish are cold-blooded, meaning they take on the temperature of the water around them, so how warm or cold the water is controls how active the fish are, where in the water they hold, and when they feed. Each species has its favorite range, and if you know the temperature, you know much more about what to expect.

In MinFangst you get an estimate of the water temperature for the place you are looking at, so you can plan before you head out. Water temperature is free for everyone.

Where to find it

• On the map: Tap a lake, and the water temperature appears in the card that opens. If you tap it, you see the estimate and can submit a reading of your own.
• In the fishing forecast: The water temperature is shown together with the weather, and it is one of the signals the forecast uses.
• On catches and fishing sessions: The water temperature is saved on the entry, so you can later see how warm the water was when you caught the fish. The figures on your entries are part of Premium.

How we calculate it

We do not have a thermometer in every lake. Instead, we work out the temperature in two different ways, depending on whether it is freshwater or sea:

• Lakes and ponds (freshwater): We estimate the surface temperature from how the air temperature has been over time, combined with the size and depth of the lake. A large, deep lake takes a long time to warm up and cool down, while a small, shallow one changes faster, and the calculation takes that into account.
• Sea and fjord (saltwater): Here we use sea temperature from the ocean model of the Norwegian Meteorological Institute.

This applies in both Norway and Sweden. To calculate for a lake, we first need to know which lake it is and how large it is, and we get that information from NVE (the Norwegian Water Resources and Energy Directorate) for Norwegian lakes and from the lake register of SMHI (the Swedish Meteorological and Hydrological Institute) for Swedish ones. The ocean model covers the whole Swedish coast, including the Baltic Sea and the Bothnian Bay.

IMPORTANT

The figure is an estimate for the surface water, not an exact measurement. It is meant as a pointer. The actual temperature can vary with depth, wind, inflow and where in the water you measure.

The water "remembers" the weather

One important point: the calculation does not only look at the temperature right now. Water has a large heat capacity and changes slowly, so the estimate is based on the air temperature over the last few months. That is why the water can be mild on a chilly morning, because the warmth lingers from the warm days before.

For the same reason we smooth the figure a little over the last few days, so it does not jump back and forth from day to day.

Trips you log afterwards

If you log a catch or a fishing session for a day that has passed, the app calculates the water temperature as it was on that day, using the same model. If you later change the date or the lake, it is calculated again. In saltwater, the sea temperature only goes back a few years, so for older trips at sea the field is left empty.

Help us become more accurate

If you measure the real water temperature in the field, you can submit it in the app. Tap the lake on the map, open the water temperature and tap Submit reading. Enter what the thermometer shows and send it. This needs a connection, and you can submit one reading per lake per hour.

Readings like these are used to fine-tune the estimate for that lake over time, and the more real readings there are, the better the calculation gets. If it says "fine-tuned on readings" under the figure, the estimate for that lake has already been adjusted. If a reading differs a great deal from the estimate, it is checked before it counts.

We also collect public bathing temperature readings (from Yr) where they exist, and use them in the same way. The adjustment is aware of the season: readings from the summer are not used to "correct" the estimate in the middle of winter.

Bathing temperatures only exist for Norwegian lakes. If you fish in Sweden, it is the readings from you and other users that fine-tune the estimate, and then each individual reading counts all the more.

TIP

If you carry a thermometer, a quick reading is a small but valuable contribution. It improves the estimate both for you and for others who fish in the same water.

NOTE

Water temperature is marked BETA in the app. It is available to everyone, but is still being fine-tuned, and will become more accurate as we collect more real readings.