Filamentous Algae ??
This pond is 100+ years old and the 50 years I have been around it has always had this problem. And some years is has been almost covered with Lilly Pads other years none. Through the years many attempts to clear the water were made but none ever worked some may have made it worse.
Things like pre-emergent herbicide, aqua shade, copper sulfate, chlorine seem to work but I did not use enough to kill fish.
The last few years it is getting worse. It is 2.2 acers when full near the dam some water is 13ft deep I would think the average would be 5ft. I am looking for an affordable solution. I have attached photos.
Delta County Texas freshwater aquaculture
Yes, you have filamentous algae, but perhaps some southern naiad as well. I recommend a tank mix of diquat (many brand names and manufacturers) and chelated copper (such as Captain XTR, Nautique, Cutrine plus, Komeen). Diquat has a good rating for filamentous algae and chelated copper algaecides have an excellent rating, so either could be used alone. However, either one used alone will not have the lethal effect that they would if you tank mixed the two herbicides (follow the directions on the diquat label for tank mixing). This combination kills the heck out of filamentous algae and southern naiad. Diquat alone will run about $225 per vegetated acre, chelated copper alone will run around $190 per vegetated acre, while the diquat and chelated copper combo will run around $350 per vegetated acre depending on the tank mix use. To treat tough filamentous algae, the diquat concentration is often reduced to between 50 and 80% of the labeled concentration when used alone, while the chelated copper concentration is reduced up to 20%, but often is added at the full concentration. The lower rates required for a thorough kill when using the herbicide mix reduce the overall costs of the tank mix.