Saint-Jean is minutes away from Gustavia, and is the most active area on the island. Its beach is split in two by the Eden Rock Hotel. The first part is near the airport and you can see the taking off and landing of small planes. You must be carefull and stay out of their way, make sure to respect the signs.
There is also an easy access to nautical activities.
The second part of the bay is on the other side of the Eden Rock Hotel : it's calmer and better suited for swimming or snorkeling.
Thank you for your understanding