Back to your original question what plane? The little Seawind EP is a nice little flyer and could probably keep up with a fast jetski if you put a high Kv motor on it. The problem is the under some lighting conditions the color scheme blends into the background and it becomes hard to see. www.modelaero.com
, makes a model called the Polaris which is a small, foam version of the Northstar. With the "hot" setup mentioned on the website the Polaris could keep up with almost anything on the lake. Since it is a "kit" it can be colored in a way to stand out against almost any background. Both of these models weigh less than 2 lbs. The little Seawind is pretty much limited to touch and goes plus basic aerobatics; the Polaris can be set up with a 1.5/1 thrust/weight ratio and guys are reporting some pretty crazy flying with it.
The big brothers to both of these models, the 71" Seawind (no longer available) and the Northstar (Balsa USA kit) both have been clocked at over 100mph with the right setup. Would probably outrun the Sheriff's boat. All four models do well with electric power, but the Northstar weighs about 6 lbs and the Seawind is on the order of 10 lbs. Spare battery packs are sort of heavy.
If you find the video on You Tube of the guy flying from the boat you will see that occasionally he needs to rotate 360 deg to follow the plane which is flying both the the front and rear of the boat he is flying from. If you were on a jetski this would be tough; you would need to be accomplished enough to keep the plane in front of you.
Back in the old days, say 20 years ago, I don't ever remember the basin being closed for the President to visit town. The 30-40 nm limit they put in (measured from Lax) is pretty restrictive. The Van Nuys Airport Cops are either a lot more vigilant or there are a lot more people provoking them; they seem to be showing up a lot more often. Add to that the fact that at least 2 or 3 times a year someone crashes a jet and burns off the brush on surrounding landscape as the fire dept. practices putting it out and you are starting to get the picture. At least the guy who used to sit on the road and access the 72 Mhz frequencies to randomly crash planes is gone. I guess that is one of the benefits of 2.4 gig.
On the other hand, there are a lot of good days too. With the Solar system the club put in for the recharging stations fuel is free if you fly electric.