The Holland Marsh is a wetland and agricultural area along the valley of the Holland River, north of the Oak Ridges Moraine and south of Lake Simcoe. The fertile soil is ideal for growing market garden crops (mainly vegetables).
Sources:
Greenbelt Plan, Schedule 3, Ministry of Municipal Affairs and Housing: http://www.mah.gov.on.ca/Asset1275.aspx
Additional Information:
Additional information on the Greenbelt Plan: http://www.mah.gov.on.ca/Page189.aspx