The beach at Pinery Provincial Park was posted as unsafe for swimming heading into the final weekend of August.
Lambton Public Health said E-coli bacteria levels were estimated to exceed Ministry of Health guidelines.
The beach is monitored weekly through water sampling with lab analysis.
The beach at Highland Glen Park is also monitored weekly, but was cleared to swim.
Grand Bend's north and south beaches, Ipperwash Main Beach, Bright's Grove (including Mike Weir Park), and Canatara Park beaches also received the all clear on Friday, August 28 using predictive models.
While no sampling occurs along the St. Clair River, caution signs advising high bacterial levels following heavy rainfall are permanently posted at Branton Cundick Park, Brander Park, and Seager Park.
