I agree its FA and Chara. But what you have is a high nutrient level which is feeding it. Can you drain it down and dry it out? If so I would do that, then dig out the sediment in the pond. The pond will be deeper and sustain less plant growth. Aeration will help clean the water but not reduce the plant growth. If you can't dig out the pond you can chemically treat the pond weeds. study what to use on this site. Then use a pond dye to limit the light getting to the bottom. However If there is a constant flow of water through the pond the dye will just wash out so you can't do that.