I have the same issue, I was perplexed as from a distance I thought it was covered in algea, which seemed odd with all of the rain, it should have been washing over the spillway. But upon closer insepection, I could see it was indeed the little plant we used to sell, if you can believe it, to home pond owners. The fish do eat it, but if you for some reason don't have enough fish, it can take over a pond. So, check your fish population and see about adding more - I think your extension agency can help with this - or TCEQ.
I'm coming off of a "fish kill" situation from a contamination 3 summers ago and was hoping the visiting wild birds would bring enough fish eggs to restock the pond naturally, but it looks like I may have to "help".
Eden's Organic Garden Center
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