These plants show heterostyly, making this definitely Nymphoides montana. Middle photos (grown out) show heterostyly: L-morph (stigma above anthers) then S-morph (stigma below anthers).
Nymphoides geminata does not show heterostyly. This is critical distinction (along with seed surface) between these two species whose distributions overlap in this region.
Otherwise, these two species are hard to visually separate.