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Species of the Month: Curlyleaf Pondweed

Jun 2023

In the early spring, many aquatic weeds form dense monocultures which can cover large areas of the water surface. These dense, pernicious growths can impede water flow in irrigation canals and restrict water-based recreation.

Curlyleaf pondweed (CLP), Potamogeton crispus, is an exotic, invasive submersed plant native to Eurasia, Africa and Australia. It was likely first introduced to the United States in the early 1800s. CLP has a very distinct appearance, noted by its wavy, lasagna-noodle leaf with serrated edges. The leaves are typically an olive green to a reddish brown and are usually 1” to 4” long and ¼” to ½” wide. There are actually two distinct populations in the U.S., identified as northern and southern biotypes.

CLP likes cold water and can even grow under ice. As the water warms later in the season (about June or July), CLP tends to senesce and die. This sudden decomposition in warm, oxygen-deficient water may result in fish kills in areas with heavy, dense infestations.

The added nutrient loading can cause issues with algal blooms, including toxic algal blooms. Due to its prolific growth, it can limit recreation for fisherman and swimmers while also impacting native plant diversity.

This weed is best managed in the spring, usually mid-April to late May, before the reproductive turions form, with the goal of reducing the plant and reproductive turions over time. Early season management also allows for a selective treatment with minimal impact to native species that are just beginning to grow.

Should curlyleaf pondweed become problematic in your water body, this invasive plant can be controlled effectively by the UPL Environmental Solutions portfolio of products, including AQUATHOL® SUPER K and HYDROTHOL® 191.

To learn more, reach out your UPL Aquatics representative by emailing