The Cowessess First Nation in Saskatchewan says it has found hundreds of unmarked burial sites near a former residential school. According to a press release issued on Wednesday, the Cowessess First Nation completed a radar scan of the area surrounding the Marieval Indian Residential School, making a “horrific and shocking discovery of hundreds of unmarked graves.” “The number of unmarked graves will be the most significantly substantial to date in Canada,” the Federation of Sovereign Indigenous Nations (FSIN) said in the release. The Cowessess First Nation is expected to make an official announcement and provide more details on the discovery on Thursday. The news comes after the remains of 215 children were discovered at former residential school in Kamloops, B.C. last month. According to the University of Regina, the Marieval residential school operated from 1899 to 1997 in the Qu’Appelle Valley. Marieval was run by the Roman Catholic Church until Cowessess First Nation took over its operations in 1981. The residential school was later demolished in 1999 and replaced with a day school.