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Walmsley Brook (named for John Walmsley, a settler in the Leaside area) started as two small streams near Duplex Avenue and Alexandra Boulevard, which joined west of Yonge Street and flowed SW to Mount Pleasant Road and Broadway Ave. From there it flowed in a generally easterly direction past the corner Bayview Avenue and Eglinton Avenue to meet the West Don River in Ernest Thompson Seton Park, just north of Overlea Boulevard. It was approximately six kilometres long and had one and a half kilometres in two tributaries. Walmsley Brook is divided into three reaches in this account: Broadway Reach, from its source to Bayview Avenue; Leaside Reach, to the CPR Railway; and Power Lines Reach, from the CPR to where it joins the West Don River. Elvina Stream, a small tributary, which joins the Broadway Reach just east of Mount Pleasant Road, and Northlea Stream, joining Leaside Reach, are briefly described.