Lake Thoreau Closed Thursday for Herbicides

Lake Thoreau will be closed to boats on Thursday so the water can be treated with aquatic herbicides.

watershed supervisor Nicki Bellezza said in an email to waterfront homeowners that the lake is experiencing dramatic growth of aquatic plants, including Eurasian Water Milfoil, Yellow Floating Heart (both non-native invasive plants) and Floating Leaved Pondweed.

The Floating Leaved Pondweed is native and is typically a beneficial plant for fish habitat and waterfowl food, Bellezza said. The Eurasian Water Milfoil is non-native plant that is of high concern.  

"We manage our lakes for multiple benefits and it is a delicate balance between ecological health, aesthetics and recreation, and the management actions required for each," she added. "We do not manage the lakes for swimming as this activity is not permitted. We have evaluated control methods of the plants -from both a budget and ecological impact standpoint. The only quick way to address this is through aquatic herbicides."

RA’s management strategy includes treating for Eurasian Water Milfoil, Yellow Floating Heart and Floating Leaved Pondweed along the shoreline and other impacted areas on Thursday.

Lake Thoreau will be closed to all lake activities including boating, fishing, and swimming all day Thursday. RA advises owners to prevent pets from entering or drinking the water.

"We have closed the lake for the treatment in order to target the plants and not have boats stir up the mud or move the plants around which would make the treatment less effective," Bellezza said.

The work will be done by a licensed aquatic herbicide company, Aquatic Environmental Consultants, Inc. It will involve applying three different herbicides to target the different plants over the course of one day.

The chemicals that will be in use: Renovate Max G, Aquathol-K, and Clean Amine. There is a restriction of no irrigation for 45 days after treatment.   

For a more informative presentation on the lakes, a water quality consultant will present a summary of water quality trends in the lakes at the July 26 RA Board meeting starting at 7 pm at the RA Headquarters office at 12001 Sunrise Valley Dr.