The latest tragedy occurred just before 8:30 p.m. Saturday in Port Colborne, when a 12-year-old North York boy began to struggle while swimming with friends at Sherkston Shores.
The boy went under the water and did not resurface. Niagara Regional Police recovered his body from the water.
Police say his family does not want his name released.
A day earlier, two siblings drowned in Port Burwell, nearly 70 kilometres southeast of London.
Ontario Provincial Police were called to the beach at Port Burwell after it was reported that three youth were in crisis in the water just before 4 p.m.
One child was rescued and pulled out of the water conscious.
The two children pulled from the water were unresponsive and airlifted to a London hospital in serious condition. They later died and the OPP have identified the victims as seven-year-old David Harder and 10-year-old Lisa Harder.
Police say the children did not know how to swim and they were not wearing life preservers when they drowned.
Fifty-three people have drowned in Ontario since the start of January. That’s slightly above the 50 people who had drowned at the same time last year.
Calls for rescue
In the eastern part of the province, the OPP reported responding to several marine calls in the Kingston area on Saturday afternoon.
A marine unit was called out to the scene of an overturned sailboat near the Marine Museum on Lake Ontario, where two people were reported to be hanging onto the side of the boat just after noon. Both of the people in the water were wearing their lifejackets.
When police arrived, the two sailors had been rescued by a pontoon boat and had already landed back on shore.
Minutes later, police were called to help out a sailboat that ran aground on Collins Bay.
Police say the people on board the boat were wearing their lifejackets and were not in danger at any time.