Neighborhood Retention pond weed control

They have aquatic formulations of glyphosate and diquat that do a good job. They are very pricey since they dissipate in the environment more quickly.
AquaNeat - glyphosate
Tribune?- diquat (I could be way off, too lazy to google)

Thank you - we had a service come and pull the vegetation out so it’s not too bad right now. Still may decide to only treat small areas at a time though because of your advice

What type of aquatic weeds do you need to control - emergent shoreline weeds, submerged aquatic weeds, .... ? Photos would help. Herbicides labeled for aquatic use are usually considerably more expensive than their terrestrial counterparts, you don’t want to be guessing on what to use without proper identication of the aquatic weeds that need to be controlled.

catch one or two small carp (just in case one of them dies) and throw them in the pond

they are grass eating machines and they will eat all vegetation in the pond until its gone and keep it gone

Yes that correct - several + generic brand names of diquat registered for aquatic use, including (and Goldbondage was correct Tribune in a diquat formulation I wasn’t familiar with). From Texas A&M AquaPlant website.

“1) Diquat

Diquat is a contact algaecide and herbicide. Contact herbicides act quickly and kill all plant cells they come in contact with.

Common trade or product names include but are not limited to:

Reward
Harvester
Tribune
Tsunami DQ
Diquat SPC2L
Weedtrine