Finely Divided

Carefully count the number of leaves in each whorl on the stem in 2 or 3 places and then chose from the following:

Eurasian Watermilfoil   Most of the whorls have 4 leaves

Low Watermilfoil l Leaves don't start from exact same location on stem; difficult to count.​

Parrot Feather   Most of the whorls have 5 leaves

If you don't think your plant is represented above try going back a level and choosing again.