Identify Plant growing in Pennsylvania Pond
Unfortunately, the photo is a bit far away from the actual plant. Can you take another photo with some of the plant in a white bucket with a small bit of water in it as well? Or, if you don't have a white or light covered bucket, if you could scoop some of the plant out and lay on a light background such as a dock or concrete. From this photo it looks like it might be filamentous algae, but I cannot be certain without a close up. Even a close up in the pond would be helpful. Thanks.
This is parrotfeather. an exotic milfoil species originally from South America. It is non-native and extremely invasive. It was likely released into the environment from folks who used it in an aquarium and has spread. It is a tough species to eradicate. The best chemical herbicide treatment for this plant is one that contains 35.3% of an active ingredient called diquat dibromide. The most popular brand name is Reward. However, local stores like Tractor Supply or Agway may have their own brand. As long as it has that active chemical in that amount it will still work. Another option is removing as much of it as you can mechanically and then treating the remainder with the herbicide. This would reduce the amount of herbicide needed and reduce the amount of decaying plant matter which can rob the water of oxygen which can lead to fish kills. To apply an aquatic herbicide you should only treat half of the pond at once and then the other half a week or two later. This will help reduce the chance of oxygen deprivation. You also need a permit to apply the herbicide.
You could also try triploid grass carp as a biological option. They do eat milfoil species.
The applications, fact sheets and instructions for both are found on the PA Fish & Boat Commission's web site. http://fishandboat.com/forms_property.htm
Let me know if you have other questions.