Does assumption of the risk apply to jet skiing?

On a warm California day, there were about 30 personal watercraft (jet skis) operating on Coyote Lake. The weather was fair and visibility good. Anthony Nguyen and Rachael Truong went for a ride on Anthony’s Polaris watercraft. Cu Van Nguyen and Chuong Nguyen (neither of whom were related to Anthony) were both riding a Yamaha Waverunner. Both jet skis permitted a driver and passenger, each seated. The two watercraft collided near the middle of the lake. Rachael was killed, and the others all injured.
Rachael’s parents sued Anthony, Cu Van, and Chuong, alleging that negligent operation of their watercraft caused their daughter’s death. The defendants moved for summary judgment, claiming that assumption of the risk applies to jet skiing. The parents appealed, arguing that jet skiing was not a sport and Rachael never assumed any risk.