Attackpoint lets you analyze your run down to quarter km splits. There's no need to take splits on your watch unless you're doing laps or hill intervals or something else fancier than km intervals. AP says you averaged a 3:53 pace in the last half km before you got onto the pier. Not bad in the heat, I suppose. ;)
I knew I shoulda hung on to that 3:45 a little longer, dammit!