In open water swim activities, just about every swim shows a best pace of about 20-30 sec/100m and corresponding max speed around 15-20 km/hr. This is undoubtedly a 'spike' in the data either caused by GPS inaccuracy, or some other transient data reading (These speeds are super-human). Oddly enough, the location accuracy for almost all of my swims is quite accurate - there are occasional 'jumps' but usually they're quite short (though it would be nice if obvious GPS errors could be filtered out)
It would be great if there was a little more smoothing or filtering of the data to remove or average out these sorts of glitches, as they make the best pace datapoint meaningless.