Canadian Waterweed
Elodea canadensis

Family:Frog's Bit (Hydrocharitaceae)
AKA: Canadian Pondweed, Common Waterweed
Photo taken on: September 28, 2019
Location: Almont Resort, GV, CO
Life Zones: Plains to foothills
Habitat: Shallow, still or slow-moving water

Grows under water with flexible stems to more than 3 feet long. Narrow leaves grow in whorls of three around the stem. Small flowers blooming in the summer produce seeds but the plant also spreads by broken fragments taking root. It can survive winter under ice. It can be invasive.

Flora of North America reference.