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Open-water swim distance differs from the track recorded? (Todays swimrun 352m vs. approx 750m, unacceptable)


Did my first open-water swim today with 955. Track looks nice and smooth, but the distance is something that makes me think.

Garmin Connect reports 3810m: 

Opened the GPX in GPXSee as wanted to have a little bit closed look and it looked like it's 4k. Umm. Upload GPX to some online tool:

What are others seeing as open-water swim distance? Does it differ from the GPX track? 

Does anyone have any ideas/explanations to give?

Here is the exported GPX if someone wants to analyze it.

EDIT: Apparently this was just a mild issue compared to todays one. Link to it: 

  • I have now new hypothesis!

    Todays swim Garmin 4576m, GPX 4640m.. But if I look it here:


    With that 1 km/h cut is 68 meters.. the difference Garmin tells and GPX distance is 64 meters.. This almost matches! Could it be that Garmin does not calculate under 1 km/h to the distance :D At least matches here.

    Then let's take some old Swimrun that was very off.. Garmin said 400m:

    No. Does not explain that, but was that OW just luck, or is the difference just because Swimrun has OW under multisport and it has at least in 945 have different algorithms. So let's check some other OW, Garmin said 4248m:

    No, does not match. Damn, almost thought that it would explain things, but no. I'll post this anyway as part of my "investigations" what could explain these, as I don't understand why we have different Distance vs. Distance in GPX.

  • I have the same problem swimm in open water. Garmin write 602m and export GPX 980m

  • And I see that it's part of multisport. Have you done OW swims without multisport? Are they more closer to GPX for you? 

    As I'm now believing that this issue is mostly affecting OW inside multisport, otherwise it's not clearly as bad.

  • next multisport garmin write 600m and export 800m , solo OW garmin write 550m and export GPX 700 ( old forerunner 945 write 750m the same hand ) 

  • Ok, little bit better but still pretty unacceptable :( So it's not just under multisport :( 

  • The track that Garmin records is pretty good yes, but for some reason the distance Garmin is reporting is not the track it recorded but something else that is the problem. And what is it reporting is the big question mark as it doesn't make any sense. Why isn't the distance the GPX track it recorded as it should be the distance, right? Now it's doing something extra to it, that is loosing distance it shouldn't be loosing. Garmin could just tell us, wtf it is doing and why and stop it, or make it optional.

    Let me show you another example:
    If I download the GPX and look that GPX has it has distance of 23582m which is probably more right than the what Garmin is reporting 19250m. I have no idea, what Garmin is reporting and what is it based upon. It is not the GPX tracks distance is recorded. I draw the route, with not so curvy lines based on the currents and I got something like 22,7k to that (ref. and then the activity itself: 

    So in my understanding accuracy is not the issue, some unknown algorithm is in play that messes things up.

  • I have now done two OW swims and both reported shorter than normal (comparing to 945, 920 and Suunto watches). I did a bridge-bridge swim I've done several times and the problem is not accuracy but the algorithm. When I stopped I did not press stop. I was standing still with the watch above water and then the watch started to increase my distance with 1-2 meter per second until it reached the "normal" distance. Then it stopped! It seems the algorithm is sort of catching-up. Something seems off with the algorithm calucating distance from the GPS track. 

  • You can upvote this bug here: Open water swim activity under report distance - Public Alpha 9.xx - Fenix 7 Family - Public Alpha Bug Reports - Garmin Forums even if a thicket was been created on 6th May... It's from Fenix 7 forum but it's the same issue.

  • Just discovered today I had the clock setting to right wrist. I do switch it from left to right during the days, but always on the left during activities. Haven't tried OW since but maybe a difference?

    Also, do you think it needs calibration in the pool to get OW right?

    Read about the Correct Distance function on Strava in another thread. Makes you look like you're not loosing it at least. Lol.

  • No difference if you set right or left wrist and there's no way to calibrate it.