Emergency crews responded to the area shortly after 4 p.m.
The driver of the Jet Ski personal water craft, Leah Herbert, 24, suffered critical injuries and was transported by Aeromed to Spectrum Butterworth Hospital in Grand Rapids.
Her passenger, Sarah Shanahan, 25, suffered serious injuries and was also transported to Spectrum Butterworth Hospital, said Sgt. Michael VandenBosch of the Ottawa County Sheriff’s Office.
Both women were wearing life jackets.
Shanahan told police that the two women were on the Jet Ski, attempting to enter the Port Sheldon channel when they lost control due to wave action and struck the pier, VandenBosch said.
The incident remains under investigation.