Mill Creek is a spring-fed cold-water stream that originates in the uplands and woodlands/wetlands of Puslinch Township, flowing south-west through the Township and the City of Cambridge, where it joins the Grand River. The upland moraine landform and the extensive Class 1 wetlands that border the creek provide important rainfall and melt-water retention and infiltration. This infiltration not only provides an important source of groundwater recharge, but also an excellent source of water that sustains Mill Creek, even in relatively dry periods. This discharge of good quality and cold temperature water supports a cold-water fishery in some reaches of the creek.
Much of the creek is still bordered by forests and provincially significant wetlands, but it has had to endure many changes over time. Early settlers dammed it for power, and these dams still block the flow and warm the water, making it harder for aquatic life to thrive in the creek. Parts of the creek were even moved when Highway 401 and Highway 6 were constructed. Forests have been removed, land has been converted to agriculture and gravel has been extracted. Fill and garbage has been put into the creek and all of this has really impeded the waterway.