The critical element that's missing, particularly in the top photo, is an object for scale.
The photographer knows the size of the leaves; but the casual viewer - myself included - probably perceives those leaves as larger than their actual size. That's why it's always beneficial to place a coin next to the plant for photo-ID purposes; for scale.
That said, my initial guess is Potamogeton diversifolius; aka water-thread, aka variable-leaf pondweed. The last common-name is derived from the plant's "variable" leaf-structures.
Look over the below images and let me know if they look like your plant. I could very well be wrong....!
PS: Note how the first two photos pose an object (a hand) adjacent to the plant for scale-reference, whereas a scale-reference is missing in the bottom photo.