Chemical treatment battles invasive weed on Halfmoon Lake

Ongoing growth of curly-leaf pondweed is affecting Half Moon Lake for swimmers and boaters


Photo by Nick Robinson

Story by Nick Robinson, Staff Writer

Curly-leaf pondweed, an invasive plant, has been a problem in Half Moon Lake for the past 100 years. This invasive plant has led to poor water quality for lake users, who are unable to swim or drive their boats in the water.

Phil Fieber, Director of Parks, Recreation and Forestry, said the explosive growth of this invasive plant comes from sawdust that was dumped into the lake.

“The phosphorus that has come from that byproduct, has been encouraging the growth of curly-leaf pondweed,” he said.

Fieber said the worst experience involving curly-leaf pondweed was during the 1970s and 1980s where the leaves were so thick it made it difficult to use the water. People weren’t able to swim or fish because the invasive plant was so thick.

Efforts have been put forth in the last 30 years to minimize the phosphorus in Half Moon Lake.

Fieber said one way of controlling this invasive plant was to apply a layer of aluminum sulphate to the lake bottom, in 2009, to cover up sediment and sawdust.

This was done to make sure the phosphorus in the sawdust and other waste materials would not be able to enter the water column and feed the curly-leaf pondweed.

“We found out that we’re going to need to reapply some aluminum sulphate over some parts of the lake because the sawdust was piled up and is concentrated in some areas,” Fieber said.

The phosphorus from the sawdust encourages the growth of curly-leaf pondweed, which grows year-long.

“For the last six years, we’ve been applying a herbicide to Half Moon Lake in an effort to kill the curly-leaf pondweed,” Fieber said. “We do it at this time of year when the water temperature is still very cool because the native plants are not blooming.”

Fieber continued by saying that the curly-leaf pondweed is thriving this time of year, and that this herbicide will continue to be used in the future in order to eradicate or get a better handle against the invasive plant and the seeds it produces.

On April 30, Half Moon Lake was treated with Aquathol K, a herbicide. Fieber said that it has been very successful used in mild doses.

“Aquathol K was used this time of year,” Fieber said. “So that there is not a direct impact on the fish or the native plants that grow in the water.”

Spring — when the water temperature is still cool and the curly-leaf pondweed is thriving — is the best time to diminish or curtail this invasive plant.

“As you have less of this invasive plant blocking the light, now the native plants that grow at the bottom of Half Moon Lake now have a chance to improve their light source,” Fieber said.

With the elimination of some of the curly-leaf pondweed from Aquathol K, the native plants have more light, and therefore, have a better chance to thrive. Fieber said the curly-leaf pondweed sucks up everything, even the oxygen from the water.

“It’s a nasty, tough plant,” he said. “It’s a never-ending battle.”