Scientific name: Hydrilla verticillata

What Is It?

Hydrilla is an aquatic plant native to Asia, Africa, and Australia. It was introduced to Florida in the 1950s through the aquarium trade. It is a tenacious weed that has several ways to propagate: seeds, plant fragments, tubers, and turions (a type of bud). It is considered one of the worst aquatic weeds in the country.

Is It Here Yet?

Hydrilla has found its way into Pipe and Lucerne Lakes, but thanks to the vigilance of the Washington State Department of Ecology, King County, and the cities of Maple Valley and Covington, hydrilla has not been seen for several years in those lakes. Continued monitoring will ensure that the plant is gone. Hydrilla has been found in a tributary of the Snake River in Idaho, which feeds into the Columbia River.

Why Should I Care?

Hydrilla can form dense stands that clog lakes, rivers, reservoirs, and irrigation canals. It chokes out native aquatic vegetation, altering predator-prey relationships among fish and other aquatic animals. The dense mats of hydrilla decrease dissolved oxygen by inhibiting the water mixing areas, increase the water temperature by absorbing sunlight, create mosquito breeding areas, and negatively affect recreation such as swimming, fishing, and boating. Once hydrilla is established, it can take millions of dollars to control each year and is difficult to eradicate.

How Can We Stop It?

Do not purchase, plant, or trade this species. Dump aquarium contents appropriately. Be sure to check boats, trailers, and motors before launching a boat to ensure there are no plant fragments that could be spread to waterways.

What Are Its Characteristics?

  • Pointed, bright green leaves about 1-5 millimeters wide and 60-20 millimeters long.
  • Leaves grow in whorls of three to ten along the stem, with five leaves per whorl the most common.
  • The leaves have small spines on the edges and at the tips and a reddish midrib.
  • The most reliable way to identify hydrilla is to look for small, white to yellowish, potato-like tubers attached to the roots, and white floating flowers.

How Do I Distinguish It From Native Species?

Hydrilla may be confused with a native plant, known as Elodea canadensis, or common waterweed. It also may be confused with another invasive species in Washington known as Egeria densa, or Brazilian elodea. You can distinguish hydrilla from these look-alike species by the presence of tubers (off-white to yellowish, pea-like structures buried in the sediment, 2/10 to 4/10 inch long). Hydrilla plants have leaves in whorls around the stem, small spines along the leaf edges, and a reddish midrib on the leaf.

Additional Photographs