Part of the Oslo agreement gives the Palestinians the right to fish 20 nautical miles out to sea. Israel violates that agreement and international law by shooting at unarmed civilians inside that boundary.
After 2006 circumstances changed and with them the law. You're more welcome to research. the LEGAL blockade permits the fishermen 3 miles, in the last years was 6. Any crossing of that is breaking the blockade and threatening Israeli territory.
Of course Israel has a stupid excuse for all of its violations.
the security of Israeli citizens is "stupid excuse" only to Anti-Zionists haters.