Apparently I caused some confusion with my posts above, here's the Cliff Notes version:

If there is NOT a specific regulation to keep a section of (or the entire) a river or stream open year round then the river/stream is closed to fishing from March 1 to the 3rd Saturday in April.

The BMA and the TMAs on the upper Housy are open year round because the regulation specifies that they are open. The other areas of the Housy from the Bleachery Dam north to the Mass line OUTSIDE of the BMA/TMA areas are closed to fishing unitl April 21st.