I have that exact same type of algae as well. I agree with the previous statements that this algae probably didn't kill your fish (since you haven't seen bunches of dead fish), but in each of my previous fish kills I had this type of algae growing all around the edges of my ponds and it popped to the surface at the same time as the fish die-off. I'd like it if Bill Cody would eventually comment if there can be any connection between specific types of dense algae mats dying and fish stress. Your water looks pretty clear, which indicates to me that if your bottom mats of algae are dying, and you don't have many single-celled alae, that you might have areas of your pond that are deficient in oxygen. Has it been calm and/or cloudy lately in your area? I wouldn't be surprised if you are currently undergoing an oxygen sag, which could make areas of your pond uninhabitable for fish. This could absolutely result in you not having any fishing success. Just because one area (or depth) of your pond is short on oxygen doesn't mean that there aren't other habitable areas, which could account for the fact that you've established there are some smaller fish available.
Welcome to the site.
Bruce
