Gaza has been, literally, a Concentration Camp for the past 75 years. Israel controls everyone who comes in or goes out through strictly policed border crossings. Israeli warships even patrol the Mediterranean coast to ensure that boats do not cross their imposed limit, either in or out.
The Oslo Accords established access to the sea for Gaza within 20 nautical miles from the shore. In the context of the Gaza–Israel conflict, the Berlin Commitment of 2002 reduced this to 12 miles. There are 4,000 fishermen in Gaza, who are constrained by the Israeli restrictions on how far they can go out to sea. They can only access a small portion of the sea, with a fishing zone limit of six nautical miles (11km) in the north and 15 nautical miles in the east.