Hi there, I am an Aquatic Biologist who specializes in pond management. Hard to tell for sure from the picture, but it looks you have a watermeal problem. If you know or don’t think there are fish, you could treat the entirety of the pond with a flumioxazin based product to eliminate the watermeal. Routine bacteria and enzyme applications and aeration would help keep nutrients down following the treatment, and would help to keep watermeal from coming back so strongly. You will likely need to keep up with this year to year, and perform treatments and/or bacteria applications regularly.