Which of the following plants is not truly aquatic but can cause problems for aquatic site managers?

Barnyardgrass (Echinochloa crus-galli) is a plant that is classified as a terrestrial grass, meaning it is not truly aquatic. However, it often thrives in wet or muddy areas, making it prevalent in environments around aquatic sites. This adaptability allows barnyardgrass to encroach on aquatic habitats, leading to several challenges for site managers. Its growth can disrupt native aquatic vegetation, contribute to diminished biodiversity, and potentially alter water quality by affecting sediment and nutrient dynamics in the surrounding ecosystem.

In contrast, the other plants listed—American Lotus, Fragrant Waterlily, and Sago Pondweed—are truly aquatic species that thrive within water environments. They are adapted to thrive in submerged or floating conditions, playing various roles in their respective ecosystems. While these plants can become problematic under certain conditions, such as excessive growth or algal blooms, they do not present the same kind of encroachment issues as barnyardgrass, which is not naturally adapted to fully aquatic conditions. Thus, the recognition of barnyardgrass as a significant concern for aquatic site managers is based on its capacity to proliferate in these sensitive areas despite its classification as a non-aquatic species.