Can you put a picture of this weed on for us to see? Identifying it will help answer your question.

Pondweed can refer to just about any kind of green thing. I get you don't know the species, but a little description would tell us something.

Things like string algae can stop green water and green water algae can also kill string algae. Just depends which can get the upper hand.

I'll try to get a pic of it.
Its a thin string with little thin tufts of green along it. But that doesn't tell you much.......so I'll try to get a pic of it.
I found a different kind in my other stocktank, so I'll get a pic of it too.
I guess I thought "pondweed" was a specific thing, but after reading up on it, there's lots of different kinds.

Maybe another approach...do you know what string algae is? We could take that off the list. What you described doesn't exactly sound like string algae.

Sounds like Nitella or maybe Chara?

Here is a link that might be useful: Nitella

Its definitely not string algae. I know what that is.
In my internet search, it looks alot like horned pondweed.
It also looks like Chara, but doesn't smell like Chara is supposed to smell.
It has formed a huge colony in my little pond. I don't mind leaving it there, if its not having a negative effect on anything.
I'm still working on pictures, but it definitely looks like the horned pondweed images I'm seeing on the internet.

These plants normally root in mud bottom ponds. Not sure if that's a clue.

Speaking generally...this type of plant is beneficial in some types of ponds and not welcomed in other types. The plant growth provides cover (from sun, from predators and ambush for predators) and and provides a good food chain base. Frogs and snakes would like it very much and have no problem. It's their home.

It would compete with other plants. Not so much O2 wise but mostly by combination of shading out to reduce growth and producing allelochemicals to kill.

O2 would be an issue for fish, but you don't have any.

As the season progresses there could be issues. Parts of the plant dies, which decays. Again depends on type pond and your goals. Plant decay in most ponds is not desired for lots of reasons, but in a wildlife pond it's a good thing. Even more creatures, many more, live on plant decay so that creates an even stronger food chain. But you also get a pond that some people wouldn't like the look of, or maybe the odor.

At the end of the season you can get a big die off and same thing, can be bad or good. A really large, suddenly dead, mass can create an environment where many creatures can't survive and you get a die off of the food chain. In natural ponds that isn't a big deal since food requirements in winter are lower. The mass of decaying plant then provides compost for the next season.

So you could split the difference and let the plant grow but trim it back as you like.

Thanks waterbug guy! You've given me lots of good info. I appreciate it!