Gull Lake Beach Park in Gravenhurst re-opened today(WED), with remaining beaches; Muskoka Bay, Muskoka Beach and Lorne Beach to open on Friday.
The beaches were closed as a precautionary measure after broken glass and needles were found in the sand and in the water.
Staff have raked surface areas and the town even brought in scuba divers to assist with the clean up.
Bracebridge beaches were also impacted but have since re-opened.
OPP continue to investigate whether the incidents are linked to a suspicious letter sent to a local media outlet, threatening the safety of beaches in Muskoka.