You have filalmetous algae. It doesn't look like it's to bad. This stuff starts in mainly shallow areas, like shown in the pic. I can be chemically controlled or raked out and put in the compost pile. I does somewhat provide a habitat for fry and minnows, but I have seen it get extremly out of control. If it stays in that small area it might be fine to leave for fry cover. Some chemicals that will control it are copper sulfate (which I no longer like to use) and Cutrin Plus, in granular or liquid form. In all cases with chemical treatment, read and follow the directions. With small amounts like you have, in my opinion, it's best to rake it out. You could dig that area deeper to help prevent it from coming back, that has worked for our pond.
