Brendan said he had a measure on it, bang on 8km.
The mud map in my brain, with a play on Google Earth, give a result of close to 3900m per lap. Plus the extra 30 metres to shore, and 20 metre sprint on shore.
When you play around with the "trapezoid" shape, all options at 3980-4000m laps don't look right.
But it was damn close to 8km.
So Woody, I agree.

(minor Edit, as Lacey grabbed my post)