Being in the Philly area, as I am, the picture you posted shows a fairly shallow stream. Depending on our weather, there is a good chance it will freeze or be very close to freezing. In which case moat of that algae will die off. Not a problem if your pond is relatively clean. You don't want a lot of organic matter in the pond in the winter. I would not recommend you leave the filter and stream running unless you are sure it won't overflow as ice builds up, and two, your fish have a deep section of pond where water is not being pulled from or disturbed.
Craig