Now that the blue lake waters are covered with a layer of white ice and the north wind sweeps across its surface, aquatic weeds may be far from your mind. However, I have just received the 2007 Highland Lake Completion Report from Aquatic Control Technologies regarding their work last summer to control the invasive weeds in Highland Lake.

You may recall Aquatic Control Technology, Inc. (ACT) began their work by conducting a thorough inspection of the entire perimeter of the lake in June 2007. The biologists prepared a map indicating the type and location of the dominant aquatic plants, both native and invasive. Next, they determined the specific herbicide treatment areas for control of the invasive species and applied to the Connecticut Department of Environmental Protection (DEP) for a permit to apply Reward (Diquat) to those weedbeds.

The ACT report indicates there were significantly reduced densities of milfoil in the shallow areas of the lake since the previous mapping was done by them in 2002; they attributed the reduction as likely due to the deep-water-level drawdown performed during the fall/winter of 2006. The greatest densities of invasive milfoil were located in the 10-15 feet of water beyond the reaches of the drawdown. Four treatment areas were identified, two at the north end and two at the south end of the lake and totaled 20-25 acres.

ACT biologists also mapped the native aquatic plant species that were mainly consisting of Naid, tapegrass and large-leaf pondweed. These plants were found in the shallow coves, and the Department of Environmental Protection does not allow them to be treated; they are part of the natural lake ecosystem, are a fish and invertebrate habitat, and are regarded as contributing to the health of a lake.

The Reward treatment was conducted on July 11, 2007 using an airboat and subsurface injection system. Aquatic Control biologists returned to the lake several weeks later to observe the results and found the milfoil had withered as predicted. On August 29, 2007, a Posttreatment Survey was conducted, and it indicated approximately 95% of the milfoil was effectively controlled. You probably were aware we had very few fragments of milfoil floating on the water, tangling in your boat motors and needing to be raked from your shorefront.

The biologists also observed the native plant growth had significantly increased in distribution and density; the growing season had been favorable for them, and the competition for sunlight and nutrients was reduced by eliminating the milfoil. In spite of this dilemma, it would be very detrimental to the lake to let the milfoil go untreated. Milfoil spreads very rapidly, forms thick mats across the surface of the water, and virtually chokes the shallow areas.

Future management recommendations include continued herbicide treatment since Reward does not kill the roots of the plants; milfoil will return next spring when another survey of their location and density has been recommended. Aquatic Control Technologies will also have to comply with requirements of the DEP Wildlife Division regarding conducting a mussel survey. Many of you provided me with mussel shells you collected from your shoreline last summer. I sent them to the DEP and was told there were five to six specimens of the Eastern Pond mussel among the hundreds they sorted through. Thus, we have been put on notice that a professional mussel survey will be required before the DEP will permit future herbicide treatment of the lake. The Eastern Pond mussel is on the DEP “Special Concern” list which is defined as “any native plant species or any native nonharvested wildlife species documented by scientific research and inventory to have a naturally restricted range or habitat in the state, to be at a low population level, to be in such high demand by man that its unregulated taking would be detrimental to the conservation of its population or has been extirpated from the state.”