Your pictures of plants outside water are a little fuzzy, but I think your plants are Chara - technically it is an algae. Clearer, sharper pictures would help. Best chemcial for Chara is Cutrine-Plus granular or some similar buffered(cheleated) copper granular. Verify it is Chara before using Cutrine. If your weed is Chara, Sonar(fluridone) will not affect it.

I prefer a "lake rake" or beachcomber rake for moderate infestations and grass carp or tilapia when the plant gets too abundant for practical raking. Both fish will eat Chara.

aka Pond Doctor & Dr. Perca Read Pond Boss Magazine -
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