Apps supporting pool swims?

To create an activity in an app, you need to use the following code to create a session.

using Toybox.ActivityRecording as Arc;
var mActivity;
mActivity = Arc.createSession( {
:sport => Arc.SPORT_SWIMMING,
:subSport => Arc.SUB_SPORT_LAP_SWIMMING,
:name => "PoolSwim"} );

Then you need to start and stop it. For my app, I used the enter button to start and stop so this is a snippet from the input delegate. mActivity is passed into the input delegate.

using Toybox.WatchUi as Ui;
using Toybox.Attention as Att;

function onKey(evt) {
.....

else if (evt.getKey() == Ui.KEY_ENTER)
{
if (mActivity.isRecording() == false)
{
mActivity.start();
mView.setBtnPress(START);
Att.playTone(Att.TONE_START);
Att.vibrate(mVibeShort);
Ui.requestUpdate();
}
else if (mActivity.isRecording() == true)
{
mActivity.stop();
mView.setBtnPress(STOP);
Att.playTone(Att.TONE_STOP);
Ui.requestUpdate();
Att.vibrate(mVibeShort);
}

Note that the simulator doesn't support starting and stopping this way. You need to start and stop the Fit Data stream manually from the pull downs in the simulator window.

Then you can get access to the available swimming data by:

using Toybox.Activity as Act;
var activityInfo = Act.getActivityInfo();

if (activityInfo.currentHeartRate instanceof Toybox.Lang.Number)
{
hrData = activityInfo.currentHeartRate.format("%d");
}

It looks like the currently available swim metrics are (page 64 of Preview 2 Programmers Guide):
//! Swim stroke type
var swimStrokeType;
//! Swim SWOLF
var swimSwolf;
//! Swim efficence
var swimEfficency;
//! Swim stroke average distance
var averageDistance;

e.g. Replace activityInfo.currentHeartRate with activityInfo.averageDistance in the code above.

I don't know if the FIT data simulator simulates these metrics or not. You probably need to create a .FIT file with these metrics in it and then playback that to get these to show up in the simulator.