I can help you ID them, just need some good descriptions or pics to confirm the ID. Basically, Look at the strem where the leaves join. Are the leaves in a rosette around the stem or are they staggered around the stem.?
If they are in a rosette them you are pretty much safe as its Elodea canadensis, if not them its likely to be the unwanted ones. As mentioned, it is probably already known that it exists in that location, and if the chance of it spreading downsteam are less likely then it probably is not a priority to clear. If risk of further distribution is high then report it immediately. Increased risk depends on how far up tributaries the location is. Near the sea then it is unlikely to spread much further downstream.