Elodea is eaten by a wide range of animals, from fish and waterfowl to freshwater snails and aquatic insects. As a soft, nutrient-rich submerged plant, it sits near the base of the freshwater food web and serves as a food source in ponds, lakes, streams, and water gardens across North America and beyond.
Fish That Feed on Elodea
Several fish species eat elodea, but carp relatives are by far the most voracious. Grass carp are so effective at consuming submerged plants like elodea that they’re widely used as a biological control tool. In managed ponds and lakes, a stocking rate of just 25 to 30 grass carp per hectare of vegetation can eliminate submerged plant growth entirely over one to two growing seasons. At lower densities, they reduce plant mass significantly without wiping it out.
Goldfish and koi, both members of the carp family, also consume aquatic plants at high rates. In water gardens and small ponds, these fish eat the leaves and stems of elodea and will uproot plants while foraging along the bottom, stirring up sediment and clouding the water in the process. Common carp are omnivores that feed on insect larvae, worms, mollusks, and zooplankton alongside the stalks, seeds, and leaves of aquatic plants like elodea.
Other herbivorous or omnivorous freshwater fish will nibble on elodea when it’s available, though they tend to be less destructive than carp species. In aquariums, for example, elodea is sometimes added as a supplemental food source for plant-eating tropical fish, though many aquarium keepers find carp-family fish will demolish it quickly.
Ducks, Swans, and Other Waterfowl
Elodea is a staple in the diet of many waterfowl. Mallards eat it readily, dabbling below the surface to pull up leaves and stems. Other dabbling ducks, coots, and swans also graze on elodea, particularly in shallow water where the plant grows close enough to the surface for them to reach. For diving ducks, elodea beds in deeper water are accessible too.
Waterfowl don’t just eat the plant itself. Dense elodea beds attract invertebrates, which in turn draw in ducks and other birds looking for protein-rich food. This makes elodea patches doubly important to waterfowl: as a direct food source and as habitat that concentrates the insects and snails birds also feed on.
Snails and Aquatic Invertebrates
Freshwater snails are significant grazers on elodea. The great pond snail (Lymnaea stagnalis), one of the most common freshwater snails in the Northern Hemisphere, feeds intensively on living elodea. Though generally considered omnivorous, these snails consume and damage living plant tissue, not just the algae coating the leaves. Laboratory experiments have shown that pond snail grazing measurably affects elodea growth, reducing the plant’s ability to spread when snail populations are high.
Other aquatic invertebrates also feed on elodea to varying degrees. Caddisfly larvae, certain species of aquatic beetles, and other small herbivorous insects graze on the leaves or use the plant as both shelter and food source. In a healthy pond ecosystem, these invertebrates collectively exert steady grazing pressure on elodea without destroying it, helping keep the plant in check.
Grass Carp as Biological Control
Because elodea can grow aggressively and choke waterways, grass carp are one of the most common tools for managing overgrowth. The stocking rate determines whether the goal is reduction or elimination. At lower densities of around 12 to 20 kilograms of fish per hectare, plant cover can be brought down to roughly 40% of its original level within a year and a half. At higher densities of 150 to 300 kilograms per hectare, submerged vegetation can be wiped out in a single growing season.
In temperate regions, effective biocontrol in the first year typically requires stocking 150 to 250 kilograms per hectare of young grass carp weighing 250 to 400 grams each. Tropical regions need less: 90 to 120 kilograms per hectare, partly because warmer water keeps the fish actively feeding for more of the year. For lakes with 30 to 50% vegetation cover, roughly 25 to 30 fish per hectare of vegetation is enough to achieve complete control of submerged plants while leaving some tougher emergent species standing.
The tradeoff is real. Grass carp don’t selectively target problem plants. They eat whatever submerged vegetation is available, including native species that support the broader ecosystem. Removing all submerged plants can reduce dissolved oxygen, eliminate fish habitat, and shift the entire food web. That’s why many pond managers aim for partial reduction rather than total elimination, adjusting stocking rates to maintain some plant cover.
Elodea’s Role in the Food Web
Elodea occupies a foundational position in freshwater ecosystems. It converts sunlight into plant tissue that feeds herbivores at every scale, from microscopic invertebrates to large waterfowl. It also oxygenates the water and absorbs excess nutrients, which suppresses algae growth and keeps conditions favorable for fish and other aquatic life.
When herbivory is balanced, elodea thrives alongside the animals that eat it. Snails graze the leaves, fish nibble at stems, ducks pull up shoots, and the plant regrows from fragments and roots. Problems arise at the extremes: too few grazers and elodea can form dense mats that crowd out other species, while too many grazers (particularly grass carp at high densities) can strip a pond bare and destabilize the ecosystem that depended on the plant cover.