distance erronée en natation. Comment modifier a posteriori sur Garmin Connect ?

Tu peux editer l'Activité et la modifier comme tu veux.

Faux, la distance reste Grisée ! Impossible de la modifier ! C’est quand même incroyable vu l'imprécision bien connue du comptage des longueurs ! Cela devrait meme pouvoir se faire directement sur connect en fin de séance. GARMIN reste sourd au propositions d’amélioration de ses users. 

Please post a screenshot of what exactly is greyed out.

You can submit your request here, if you have not done this already - https://www.garmin.com/en-US/forms/ideas/. No guarantees it will be implemented, but if enough similar requests are made, they might take notice.

While you wait, you can edit swimming activities here - www.swimmingwatchtools.com

Additionally, if you change the activity type to a different GPS activity, such as running, then you might be able to use the "trim" feature in Garmin Connect Web. Then change it back after the distance is edited.

2537193 said:

The distance is grey and cannot be changed

You need to change the number of pools, not the distance. The distance will be recalculated automatically.

Open the activity, tap Edit, scroll down, tap More Data, modify the number of pools, save.

Thanks for your reply. However the minimum swimming pool length you can save is 14 meters and I need 10 meters. How can we go down to 10 meters on the watch

You can't. Make it double (20m), and divide the number of lengths by two.

I agree but when I synchronise I will have a wrong distance (twice the real distance). This is the reason why we should be able to change the distance aftzr synchronization 

As I wrote, you will have to edit the activity and divide the numer of pools by two.