No there is no doubt the waterskiing harvards are real...many witnesses and the pilots too well known for it to be faked. My only point is they must have practiced quite extensively, both solo and together, before submitting to the photo flight....information on a SA website suggests the actual pass down the lake that is the subject of the photos was one of 5 that day....lots of people there watching...all very well planned....apparently.
On a thread on Private Flying forum there is a picture of two Jodels waterskiing in formation and I have seen another of two cubs waterskiing on formation...this particular 'art form' is a lot more widely practiced than I thought.
While not essentially difficult to achieve it is a pastime fraught with potential embarassment.
It is all based around the basic aquaplaning formula...9X square root of the tyre pressure. Clearly there is also some benefit from really big tyres like the Tundra tyres you see on some back woods cubs etc...then it is more like plane waterskiing....although even at very low tyre pressure like tundra ones you have an aquaplaning speed of only about 25 knots...so any faster and you are happily waterskiing.
If you don't have the brakes on you risk wheel spin up which probably wont, you hope, effect the aquaplaning formula (if you are travelling really fast) but will spray a lot of water all over the place.
If you hit something solid in the water you risk being tripped and flip over...remember when we hit that cable on our forced landing in Moresby. It hit about half way up the tyre and we nearly went over, but we ripped it out of the ground a split second later
....even so our nose down attitude would have guaranteed the prop/nose impacted the water had we been waterskiing instead of 50+' above the road.
If you are not very carefull rotating to leave the water you may dip the tailwheel in the water or at least put the rear of the aircraft (horizontal stab) in the plume possibly slowing down enough that you almost stop aquaplaning and drag rises...quickly flipping you over.
The actual act of putting the aircraft on the water is the easy part...once you get over the pucker factor. The list of things that can go wrong after that gets a little scary....more so in a light/relatively underpowered aircraft like a cub than heavier/faster/more powerfull aircraft like a C185/Harvard....I would think.