The marshes are along the Humber River between Queensway and Bloor. Unless you happen to know someone living along Riverside Drive or Riverside Crescent (off South Kingsway), the only way to access them is by boat. This year, with the low water levels, access is limited and difficult.
There are several places to launch a boat, but my preferred spot is off South Kingsway, just north of the Queensway. There's a small lot just south of the gas station - very easy to miss.
BB