This guide to curly-leaf pondweed covers its origin, current distribution, description, biology & habitat, threats & impacts, spread prevention, control methods, and common native look-a-likes.

Origin

Curly-leaf pondweed is native to Eurasia, Africa, and Australia. 

Distribution

The first documented occurrence of the plant in North America was in Philadelphia in 1841-1842. By 1890 it had been confirmed in Deleware, Massachusetts, New York, and Ontario. By 1950, Curly-leaf pondweed was established across much of the United States and eastern Canada. The plant is now found in all 50 states and much of Canada. 

Description

Curly-leaf pondweed is a rooted submerged aquatic plant. It has green to reddish-brown oblong leaves that follow an alternate pattern. One of the primary identifying characteristics is the wavy leaf margins that resemble the edges of a lasagna noodle and have serrated edges. Leaves are a half-inch wide and up to three inches long and increase in density towards the end of the stem. The mainstem can vary in color (white, brown, or green) and often branches near the top of the plant. The leaves may be bunched near the water’s surface but are not floating. 

Biology & Habitat

Curly-leaf pondweed grows in shallow near-shore, or littoral, areas of lakes to depths of approximately 15 feet. It tends to become established in disturbed areas and can tolerate low water clarity due to nutrient pollution and runoff. 

Curly-leaf pondweed blooms in June with flower stalks that emerge above the water’s surface, though its primary mode of reproduction is through the production of turions. Turions are buds that are capable of producing an entirely new plant. Curly-leaf pondweed has a unique adaptation that gives it a competitive edge over native plants; its turions begin to sprout and grow in the late fall to early winter, whereas most other plants are dormant this time of year. As a result, when spring comes around and ice goes out, curly-leaf pondweed is mature and can quickly outcompete native plants. Though, the plant tends to die back much earlier in the season than native plants. 

Threats & Impacts

Curly-leaf pondweed has the potential to impact both the recreation and ecology of lakes and ponds that it invades. One of the more troublesome impacts for lakeshore residents and visitors is that it can grow in dense mats extending to the water’s surface, and these mats can be challenging to boat or even paddle through. As a result, opportunities for boating and other forms of recreation that many people enjoy can be impacted. For example, in the North Arm of Hayden Lake in Idaho, curly-leaf pondweed grew so dense that it bound up boat propellors and choked out local swimming holes. 

Curly-leaf pondweed is also associated with declines in water quality, especially in small shallow ponds with little native vegetation. The life-cycle of curly-leaf pondweed results in senescence or dye back in early to mid-summer. When this occurs, the plants decompose, resulting in declines in dissolved oxygen through increased aerobic bacterial decomposition. In addition, the breakdown of the plants can release nutrients in the water and spur algal blooms. 

Dense beds of invasive aquatic plants can also negatively affect fish populations and alter aquatic food webs. Prey fish can more easily hide among the thick pondweed beds, making it more challenging for larger predatory fish to feed on them. Shifts in diet can reverberate through the aquatic food web as fish alter their feeding strategies and consume groups of organisms they otherwise would not. 

Spread Prevention

The key to avoiding the negative impacts of curly-leaf pondweed is to prevent its introduction into new lakes and ponds. The primary mode of the spread between water bodies is on recreational boats and their trailers. Follow the Clean, Drain, Dry principles whenever launching or retrieving your boat from a lake or pond. 

1. Clean all dirt, debris, and plant matter from your boat, trailer, fishing equipment, and other water-related gear.
2. Drain the bilge, engine, and all compartments of water.
3. Dry your boat for at least five days before launching in another waterbody.

Following these simple steps will prevent the spread of curly-leaf pondweed.

Control Methods

Once an aquatic invasive plant like curly-leaf pondweed makes it into a waterbody, it can be challenging and costly to control. The most common control method is through some form of physical harvesting of the plant. 

Hand-harvesting: Trained divers’ hand-harvesting the plants is one of the most effective management options. This option can be both time-consuming and costly but has the advantage of being targeted and removing the plant and its root system. Because divers can identify and only remove curly-leaf pondweed, this leaves any native plant species at the site intact and undisturbed, giving them a chance to become re-established. Removing both the plant and its root system limits the potential for regrowth later in the season or the following year. 

Diver Assisted Suction Harvesting (DASH): This is very similar to traditional hand-harvesting but uses a dredge set up to help transport the plants and their root systems to a processing station on a boat. This system requires more investment than hand-harvesting but improves the efficiency of the operation, allowing for more areas to be covered. 

Mechanical Harvesting: Various mechanical plant harvesting machines can pull plants out of the water. They can process large areas quickly but have several downsides:

1. These harvesters are not targeted or selective, meaning they cannot target only the invasive plants within the area harvested.
2. They don’t always get the plant’s root, allowing for regrowth later in the season or the following year.
3. They can result in plant fragmentation, which for many aquatic invasive plants, is one method by which they spread.

Mechanical harvesting is typically only a good option where boating is being impacted, and the curly-leaf pondweed bed is so large there is no hope of controlling or eradicating the plant with other approaches. 

Herbicides: In a limited set of circumstances, aquatic herbicides may be used to control curly-leaf pondweed. Many factors must be considered, including the size of the area being treated, the biomass of the plant bed, the flushing rate of the pond or bay being treated, impacts on native plants, and impacts on drinking water and swimming. A lake manager often completes the planning process and will require extensive permitting depending on state and local laws. 

Common Native Look-A-Likes

Pondweeds are a diverse group of aquatic plants common across North America, and these native species have many beneficial effects on lake and pond ecosystems. Depending on where you are, there are several native plant look-a-likes. 

• Narrow-leaf pondweeds will have leaves narrow like those of curly-leaf pondweed, but they won’t have the wavy lasagna pattern or toothed edges.
• White-stem pondweed has a wavy pattern to its leaves, but they are broader and do not have toothed edges.
• Clasping-leaf pondweed looks similar to white-stem pondweed, but the leaves clasp or surround the plant’s stem. This is a characteristic not found on curly-leaf pondweed.
• Broad-leaf pondweeds have much broader leaves than curly-leaf pondweed and lack serrated edges.

Taxonomic Information

• Kingdom: Plantae
• Phylum: Magnoliophyta
• Class: Liliopsida
• Order: Najadales
• Family: Potamogetonaceae
• Genus: Potamogeton
• Species: Crispus

Sources

• Distributional history of Potamogeton crispus (curly pondweed) in North America
• Curly-leaf pondweed trends and interrelationships with water quality
• Effects of curly-leaf pondweed (Potamogeton crispus l.) biomass on eutrophication in Baiyangdian Lake
• The role and interactions of submersed macrophytes in a shallow Wisconsin Lake