Emergency crews were called to the river in Dunnville on Tuesday afternoon after the human remains were found, and police initially thought the girl was between one and four years old.
He said police are working with the Grand River Conservation Authority to figure that out.
They're also combing through missing-persons cases beyond the sleepy town about 55 kilometres southeast of Hamilton, close to where the Grand River meets Lake Erie. .
Maggie Cole, 27, manager of Queens Merritt Room, a restaurant close to the riverbank where police were searching this week in the town of 12,000, called the discovery "very sad news." .
Police said Wednesday the remains appear to have been in the water for some time and they don't believe there is a threat to public safety.
Earlier in the week, members of the OPP's search and recovery unit could be seen in the area, with officers on a boat, on shore and in the water combing the river.
Wasyl Luczkiw, 28, whose family owns the Grand River Marina and Cafe, said police initially used the business's property as a staging area and used one of its boats to search before bringing their own.
The marina is across the river from Queens Merritt Room, on an island in the river.
The Grand River runs from Dufferin Highlands, north of Guelph, to Lake Erie, stretching about 310 kilometres in total.
The <a href="https://twitter.com/hashtag/HaldimandOPP?src=hash&ref_src=twsrc%5Etfw">#HaldimandOPP</a> Crime Unit, under the direction of the Criminal Investigation Branch, continues to investigate the discovery of the body of a child in the Grand River on Tuesday
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