Yeah that's water primrose or Ludwigia (especially if it has pretty yellow flowers). Reproduces from seeds and fragments and is a knotted mess if left alone.
I'm here in San Marcos with the Lake Mower company if you're interested in a mechanical option.
If at first you don't succeed...look in the trash for the directions.
The correct chemical for yellow water primrose is a Glyphosate (like Roundup) that is pond friendly. The best surfactant is Cide Kick but I recently used Spreader Sticker with good results. Diquat also will clobber it. You can get the chemicals from tractor Supply Company but I had to look elsewhere for a surfactant.
It's not about the fish. It's about the pond. Take care of the pond and the fish will be fine. PB subscriber since before it was in color.
Without a sense of urgency, Nothing ever gets done.
Boy, if I say "sic em", you'd better look for something to bite. Sam Shelley Rancher and Farmer Muleshoe Texas 1892-1985 RIP Grandpa