With the new Apple Watch Ultra, and WatchOS 9.1, is possible to use the new Action Button to start Waterspeed and immediately Start a new activity, Pause, Stop, or Start a Countdown (you need to setup the countdown activated from the Settings).

DEFAULT SPORT: the app will start the latest sport chosen. If none, the first in the list. Please, start manually a sport once, to set as the default for the Action button.

For Countdown: after starting, if press the Action button again, it will perform 'Sync -'.

PAUSE: If the activity is started, press Action Button + Side button to Pause.

RESUME: If the activity is Paused, press Action Button to REsume

STOP: If the activity is Paused, press Action Button and Side button to Stop.

Be sure to configure the Action Button in the System Settings of your Watch: