A 16 km loop is just about right for me on my long days. Starting in North Glenmore Park is my usual starting point but South Glenmore Park or Heritage Park are good starting points too. There is a paved multi-purpose pathways the whole way. Occassionally there are pedestrian only paved pathways too.
The single-track is along the water, and in Weaselhead Flats (west end of the Reservoir). Weaselhead is an especially good place to get lost for a while (not literaly lost but that is not hard to accomplish in these isolated trails).
In the summer there are sailing boats and canoes on the water, and lots of bikes on the trails. These days it is much quieter in the park, but it is still busy on the weekends.
Map of Park here
More Park info here