The Capitol Region Watershed District will inject fluridone, an organic aquatic herbicide, into Como Lake in St. Paul to fight curly-leaf pondweed.

The fluridone will be used against the invasive plant two days in April before it begins reproducing, according to the District 10 Como Community Council.

Curly-leaf pondweed is not native to North America and was likely introduced in the late 1800s when common carp were brought to Midwest lakes as a game fish, according to the Minnesota Department of Natural Resources.

The plant is the main cause of Como’s declining water quality and summer algae blooms. It grows under ice in the winter, unlike native plants, and now makes up about 90% of the lake’s plant life.

When curly-leaf pondweed dies in late June, it creates mats on the water’s surface that release phosphorus into the lake, causing bad smells and a poor habitat for fish and other lake creatures.

In May, the watershed district will inject aluminum sulfate in the lake to reduce phosphorus levels. The watershed district hopes to continue treatments for up to seven years to reduce curly-leaf pondweed enough to give native plants a chance to reclaim the habitat.

The low concentration of fluridone to be used in Como, 4 parts per billion, has no known effects on people, pets or wildlife, according to the council.

J.D. Duggan ( is a University of Minnesota student on assignment for the Star Tribune.