Nizar Ayyash of the Gaza Fishermen's Union says the incident occurred today off the northern Gaza town of Beit Lahiya.
Israel recently doubled the maritime area in which Gaza fishermen are permitted to operate from five to nine kilometers (three to six miles).
The Israeli military says it's looking into the report. Israel and Hamas-led militants in Gaza ended 50 days of intensive fighting on August 26 and committed to enter into indirect truce talks in Cairo aimed at developing a sustainable roadmap for the future of the densely-populated coastal territory.