Curly-leaf Pondweed in Lake George

Photo courtesy of: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

This invasive aquatic perennial is native to Eurasia, Africa, and Australia. It was accidentally introduced to United States waters in the mid-1880s by hobbyists who used it as an aquarium plant.

Click here for a fact sheet on Curly-leaf pondweed (Potamogeton crispus) - pdf.

Description
Leaves are somewhat stiff and crinkled, approximately 1/2 inch wide and two to three inches long. Leaves are arranged alternately around the stem, and become denser toward the end of the branches. Curly-leaf pondweed produces winter buds; it can be confused with clasping leaf pondweed. The leaves of curly-leaf pondweed are reddish-green, oblong, and about three inches long, with distinct wavy edges that are finely toothed. The stem of the plant is flat, reddish-brown and grows from one to three feet long. The plant usually drops to the lake bottom by early July.

Hints to Identify
- Has small "teeth" visible along edge of leaf;
- Begins growing in early spring before most other pondweeds;
- Dies back during mid-summer;
- Flower stalks, when present, stick up above the water surface in June;
- Appears reddish-brown in the water, but is actually green when pulled out of the water and examined closely.
- Easily confused with clasping leaf pondweed, which has leaves with no "teeth" around its edges.
- Looks like lasagna noodles, and if you swim through it - it will feel scratchy because of all the teeth along the edge of the leaves.

Distribution and Habitat: Curly-leaf pondweed is commonly found in alkaline and high nutrient waters, preferring soft substrate and shallow water depths. It tolerates low light and low water temperatures.

Curly-leaf pondweed invasion. Photo courtesy of: Chris Evans, River to River CWMA, Bugwood.org

Life History and Effects of Invasion: Curly-leaf pondweed spreads through burr-like winter buds (turions), which are moved among waterways. These plants can also reproduce by seed, but seeds play a relatively small role compared to vegetative reproduction through turions. New plants form under the ice in winter, making curly-leaf pondweed one of the first nuisance aquatic plants to emerge in the spring.

It becomes invasive in some areas because of its tolerance for low light and low water temperatures. These tolerances allow it to get a head start, out-competing native plants in the spring. In mid-summer, when most aquatic plants are growing, curly-leaf pondweed plants are dying off. Plant die-offs may result in a critical loss of dissolved oxygen. Furthermore, the decaying plants can increase nutrients, contributing to algal blooms, and they can create unpleasant stinking messes on beaches. Curly-leaf pondweed forms surface mats that interfere with aquatic recreation.

Control Methods: Turions and plant fragments can be carried on boats, trailers, motors and fishing gear from one waterbody to another; proper prevention techniques are essential to curb the spread of this aquatic invasive. An effective prevention and remediation program also addresses the overall health of a waterbody. Maintaining a healthy ecosystem with diverse native aquatic plants and animals, as well as minimizing nutrient and pollutant inputs, will deter invasions. Once introduced, curly-leaf pondweed spreads rapidly. Long-term management requires the reduction or elimination of turions to interrupt the lifecycle.

Source: www.ci.elk-river.mn.us; www.dnr.wi.gov

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