Curly-Leaf Pondweed

What is curly-leaf pondweed?

Curly-leaf pondweed is a non-native, rooted underwater plant that has been in North American waters since the mid-1800s. curly-leaf pondweed identification relies on its leaves: wavy, crinkled blades with finely toothed edges and blunt tips, olive-green to reddish-brown, set directly on the stem. Its odd calendar is another clue, since it grows through winter and spring and largely disappears by midsummer.

That calendar is also why it causes trouble. Starting early lets it form dense mats in spring that shade out native plants and get in the way of boating, swimming and fishing. When it dies back in midsummer, the decaying plants release phosphorus that can feed algae blooms, and the rotting algae can then pull oxygen out of the water. It can also clog irrigation canals.

Curly-Leaf Pondweed identification: what to look for

Pull up a strand and look at a single leaf against the light. Curly-leaf pondweed's leaf edge is both rippled and finely toothed, while its native look-alikes have smooth edges. In early summer, also check for turions, the hard little pinecone-like buds.

• Leaves: Alternate, stalkless and crowded toward the stem tips, about 3/4 to 3 1/4 inches long and up to 1/2 inch wide, with a clear midvein and a rounded tip.
• Leaf edges: Wavy like lasagna noodles and finely toothed. The teeth are the key feature; native look-alikes have smooth edges. Young leaves may be flatter but are still toothed.
• Stems: White, green, brown or reddish, branching several times near the top. Plants can mat at the surface, but there are no true floating leaves.
• Flowers: A small reddish-brown spike, about 1/2 to 1 inch long, that pokes above the water around June.
• Turions: Hard, brown, bur-like buds about 1/2 to 1 inch long, resembling tiny sharp pinecones. They form in late spring and early summer and sink to the bottom.

Where it grows in the United States

Curly-leaf pondweed has a long history here. The earliest verified North American collection dates to Philadelphia in 1841, and Wisconsin DNR says it spread through the Northeast and Great Lakes by the early 1900s. Minnesota DNR suggests carp stocking may have carried it into Midwest waters in the 1880s. Today it reaches from coast to coast, including the Northern Rockies, where Montana first recorded it in 1973.

It grows in lakes, ponds, reservoirs, streams and rivers, tolerates moderate current, and is most common in alkaline, nutrient-rich water. It handles murky or disturbed water where other plants struggle, and growing under the ice gives it a head start on natives each spring. Boats and trailers carry it between lakes.

Curly-Leaf Pondweed look-alikes

A few plants get mixed up with it:

• Richardson's pondweed (Potamogeton richardsonii): A native with somewhat longer leaves (about 3/4 to 4 inches) that have pointed tips and smooth, untoothed edges, on a slightly flattened, branched stem.
• White-stemmed pondweed (Potamogeton praelongus): A native with much longer leaves (about 2 1/2 to 8 inches), pointed tips and smooth edges, on a round stem that often zigzags.

How to get rid of curly-leaf pondweed

Pulling, digging and mowing: Raking, hand-pulling and cutting can clear swimming areas and docks. Montana State recommends doing it in spring to early summer, before turions form, and repeating for years; one Montana group raked three straight years before the patch could simply be monitored. Light-blocking bottom barriers around docks work well but are costly and smother natives too, and fall or winter drawdowns can freeze turions where water levels can be controlled. Wisconsin DNR cautions that mechanical removal gives one season of relief at most and can harm native plants and fish. Minnesota and other states require a permit to remove plants from public waters.

Cultural control matters most, because the right conditions keep it from coming back.

• Clean, drain and dry: remove plant bits from boats, motors and trailers, drain all water, and let gear dry several days (Minnesota requires 21 days for docks and lifts moved to new waters).
• Never dump aquarium or water-garden plants into natural waters; seal them in a bag and trash them.
• Where permitted, plan water-level drawdowns in fall and winter to freeze turions.
• Grass carp are used in some places, but they eat native plants too and damage habitat; they are prohibited in Montana.

Herbicides: Endothall is the most commonly used herbicide; Montana State also lists diquat and fluridone, noting fluridone works slowly and must be applied lake-wide. Treat in early spring, while plants are actively growing in cool water, natives are dormant and plant mass is low, which also limits the phosphorus released as plants die. Wisconsin DNR notes that depleting the turion bank takes several years of early-season treatment, costs a lot, and that small endothall spot treatments disperse too fast to work well. Herbicide use in water usually requires a state permit (Minnesota and Wisconsin require one), and in Montana only licensed aquatic applicators may treat water. Use only products labeled for aquatic sites and follow the label; it is the law. If you hire someone to spray, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Keeping it from coming back

The best defense is keeping it out. Turions and fragments ride on boats, trailers, docks and gear, so clean everything, drain all water, and dry equipment before moving to another lake or pond.

If it is already present, early action pays. Catching a new patch before it builds a turion bank keeps control smaller and cheaper. Report new finds to your state natural resources agency or EDDMapS.

Questions we get about curly-leaf pondweed

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