I found something while finding the 99th red balloon!!!
I went around the other side of the lighthouse and found a Sanchez, and since I'd just driven my Sabre into the water I hopped on and it triggered a vehicle triathlon called "Land, Sea, and Air Ace". I "aced" it on my second time; you use the Sanchez, the Jetski, and the Sea Sparrow to pass a variety of checkpoints. It was pretty fun and won't take you more than 3 tries to beat (Very little trial and error). Just though you might want to add this to your 100% guide Slim!