Myriophyllum plants can be tricky to identify, as there are three that are very similar. This plant has emergent leaves in whorls of at least 5 maybe more: this rules out M. simulans (typically in whorls of 3-4) and makes M. variifolium doubtful (typically in whorls of 5) and suggests it could be M. crispatum (emergent leaves in whorls of 6 to 9). If it is M. crispatum, then it would likely have crisped hairs on the stem, but no sign of these in photo. So confirmed s Myriophyllum sp. If it is M. crispatum, then its an interesting sighting for this area: