The marina consists of three small buildings at the riverside. There are no opponents here.
In the biggest house, you meet Phyllis. Thanks to the conversation with her, you can turn this place into a settlement. There are several ways in which you can convince her: with Charisma level is sufficiently high, during the conversation; by reading her journal in the terminal at the upper floor, after which you talk to her; while you are a Minuteman faction member, you can simply kill her. Regardless of the approach you adopt, the result will be the same - you will be able to use the workbench.
In the hangar, opposite the house, there is a safe with advanced lock. It is in the boat suspended under the ceiling. Next to the safe, there also is an ammunition box.
In a small building at the marina, you find quite a supply of food and an issue of Wasteland Survival Guide.