Waterweed

Waterweed is a common name for several freshwater aquatic plants that grow submerged in streams, lakes, ponds, and often in aquariums. It does not refer to a single species but to a group of plants, most commonly Elodea and Egeria species, as well as Hydrilla. Examples frequently encountered in temperate to tropical regions include Elodea canadensis (Canada waterweed), Egeria densa (Brazilian waterweed), and Hydrilla verticillata.

Waterweeds are typically perennial aquatic plants with slender stems and leaves arranged in whorls or opposite pairs along the stem. Leaves are usually small and linear or oval, adapted to life underwater. Growth can be rapid under favorable light and nutrient conditions, and several species can spread vegetatively through fragments, making them efficient colonizers of suitable habitats.

Ecology and impact: Waterweeds provide habitat and grazing opportunities for aquatic invertebrates and small fish, and they can help stabilize sediments and oxygenate water. However, when introduced outside native ranges, they frequently form dense mats that shade out other vegetation, reduce biodiversity, and hinder boating, fishing, irrigation, and drainage. Their spread is often aided by fragmentation, seed production, and, in horticultural contexts, release from cultivation.

Management and use: Waterweeds are valued in aquariums and water gardens for rapid growth and water purification. In wild ecosystems where they are invasive, management includes mechanical removal, shading to limit regrowth, and, where appropriate and regulated, targeted herbicide use. Prevention of new introductions and rapid response to emerging infestations are important to minimize ecological and economic impacts.