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Hydrilla forms large, dense populations that disrupt ecosystem functioning, displace native aquatic species, and impair fish and wildlife habitat. Hydrilla out competes native vegetation and provides poor habitat for fish and other wildlife. Dense mats alter water quality by raising pH, decreasing oxygen under the mats, and increasing temperature. Loss of oxygen can result in fish kills, depleted fish populations, and reduced fish size.

Eurasian watermilfoil is a submersed, rooted, perennial dicot. The stem branches underwater and produces many whorled, finely divided leaves near the water surface. The leaves can have a grayish cast and feathery appearance. Eurasian watermilfoil is one of several aquatic invasive weeds that reproduce primarily by fragmentation. This species is tolerant of low water temperatures, quickly grows to the surface forming dense canopies that shade out surrounding vegetation, and can form thick underwater stands of tangled stems.

Brazilian elodea can be rooted to bottom sediments in depths of up to 20 feet. Its leaves are 1 to 3 cm long, up to 4 mm broad, and are in whorls of four to eight. The rapid growth rate allows it to cover water surfaces and displace native vegetation, causing interference with normal development of fish and wildlife habitat by the formation of impenetrable mats and decreased water flow.

Coontail is a submersed plant, it has no roots and so is free-floating. Because its feathery leaves are arranged in whorls on the stem, this plant resembles a racoon's tail. They look feathery because each leaf is divided into many narrow segments. Each leaf has several small teeth on the midribs, they give the plant a rough feel when pulled through the hand.

Giant salvinia is a free-floating fern with irregularly branched stems and an absence of roots. Its leaves, which are actually fronds, are in whorls of three, two floating and one submerged. It reproduces aggressively by vegetative propagation. New plants quickly develop as fragments break off from mature individuals. Giant salvinia is considered to be one of the world's worst invasive aquatic weeds. It is an extremely aggressive, competitive species that in favorable environments may double in size within about a week that can result in complete coverage of water surfaces, which degrades natural habitats.