A closed-toe swim fin device. The swim fin includes a rear cavity designed to receive the front portion of a user's foot, e.g., the portion in front of the ankle, and to hold the user's foot therein via vacuum seal, friction, and pressure fit. The swim fin is otherwise sealed and fluid-tight such that the only way into and out of the rear cavity is through the rear cavity's opening that receives the user's foot. In this way, the swim fin eliminates the need for other types of foot attachment mechanisms (e.g., shoes, heel straps) thereby reducing the resulting water drag of the fin when in use.