From locality, I would expect to find Myriophyllum variifolium as you suggest. However, it has emergent leaves in whorls of 5 typically, so 3-4 is unusually low. is this count for the pectinate leaves (which are actually transitional leaves)or the entire leaves just visible ?
Ok it seems like what i've done is got myself confused with the key couplet separating this from M.simulans. My video note shows a count of emergent leaves in whorls of 5.