How to go to the island with gta5? How to investigate from the airport?

The enclosure at the beach party seems to be very low, but there is an air wall motorcycle that can't fly through, and then I come to Location 2. There is a high sentry, a ground patrol and a monitor at this intersection. When the two people leave a gap in their vision, I can leave it directly behind the house from under the monitor. Let's explain again that the fence of this site 2 extends to the sea on both sides, so you can only cross here, or you can only swim in the sea. If you are really stupid, you can swim from the beach party, bypass this checkpoint, and never swim from the fence of the checkpoint, because there is no place to land there.