Calories burned during swim are incorrect

I have not had that issue (non-swimmer) but I recall there being a post about this.  Was part of a general calorie issue iirc, couldn't find it.  might be in the general  Running/Multisport forum under accessories/sensors (the only other forum i view regularly)

Thank you for the quick reply NickMN, I will search the other topics!

That's not bad, I got once for an easy swim 4400 calories. I still don't know what could've caused it. Next time I got a more believable 400

Thank you flocsy, so hopefully it’s just a one off.

i started searching for answers and find people having similar issues. New to Garmin world, been about few months now. my 1.5k swim showed around 450 cal and today 1.5k swim showed around 1447 Cal. I find the first number to be true, as my 1k swim normally shows around 250 to 300 cal. Will check out another 1.5k to see if it was just one off.

I believe my kcal calculation is still "correct". Usually around 550 kcal for one hour session. That is mostly like 2800-3200 meters and 50 min active time (non rest) +- .
If you are using a chest strap Firstbeats' algorithm will be used. Otherwise 

• Length of time

• Body weight

• Swimming speed

• Swim stroke type

Wrist pulse will not be used. I have used chest strap sometimes in pool but don't like it. It is okay under a wetsuit or a swimskin doing OW is my opinion. 

Why do you think wrist HR is not used?

They say that they don't use it. I guess that Garmin determined that wrist data is not reliable enough. 
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How Accurate Is the Wrist Heart Rate When Swimming?

Swimming can have many of the challenges which are described in The Heart Rate Sensor on My Garmin Watch Is Not Accurate. The large arm motions can affect the level of blood volume in the wrist area, chilly water can reduce the amount of blood in the tissue on the back of the wrist, and the water can “pull” on the watch creating a gap between the optical heart rate sensor and the skin. The same tips apply to swimming as other types of activities. Warm up a bit before starting the swim activity and make sure you are properly wearing the watch. Specifically:

• The optical heart rate sensor must always remain in contact with your skin.

• The watch must also be worn snug, but not too tight.

  • Too loose the watch can slide around, creating a gap between the optical heart rate sensor and your skin.

  • Too tight and the watch can actually restrict blood flow.

• The watch is properly snug when you can move the watch and the skin underneath moves with it.

For best heart rate accuracy during swimming, use the HRM-Pro, HRM-Pro Plus, HRM-Swim, or HRM-Tri.

On the contrary! The above does say that they do use it! If they weren't then they wouldn't give the tips how to improve it!