2019-2020 Sixth and Seventh Lakes Invasive Species Survey

Executive Summary

The 6th and 7th Lake Improvement Association (Association) commissioned a study of aquatic invasive species present in our lakes.  The study was conducted in 2019 and 2020 by the Paul Smiths College Adirondack Watershed Institute (AWI), and was underwritten by Association contributions collected specifically for mitigation of invasive species.  The full report is posted on the Association website, https://sixthandseventhlakeassoc.org/

The study confirmed the fact that invasive plant species, principally Eurasian-water milfoil and variable-leaf milfoil, remain present in our lakes.  The good news is that the presence of these plants is limited and appears not to be spreading.  A prior plant survey done in 2010 gave us a good baseline, and this most recent survey conducted in September 2019 shows that the extent of infestation is actually no worse than what was identified in 2010. 

The report includes figures that show the location and density of the invasive species throughout both lakes.  These areas tend to be near shore locations, and in the small bays and inlets around the lakes.  The most notable location is on 6th Lake near the dam.  Also notable, there are no invasive plants near the 7th Lake boat launch which is a good sign and evidence that the boat inspection process is working well.

Overall, while invasive plant species are present in our lakes, the situation is generally benign and has not reached a point of diminution of lake usage and water quality.   By comparison, there are areas in the lower lakes, Old Forge Pond through 5th Lake, where waterfronts are rendered unusable and inlets are completely clogged with invasive species and other weeds – that is the situation we need to avoid.

The report also outlines potential strategies and costs for mitigation.  These options includes “whole lake” mitigation as well as other, more localized control options.  It is important to note that complete eradication is not practical or possible – this is something we have to live with and the decision here is to what extent we need to exert control over this situation.

Another significant factor that is working in our favor is the annual lake drawdown which exposes portions of the near-shore lakebed where some of the invasive plants are exposed to freezing temperatures and die off.  This, in combination with our ongoing stewardship activities, is another reason why our infestation remains stable.  The lake drawdown aspect becomes even more intriguing by the fact that the Hudson River Black River Regulating District (HRBRRD), who owns and operates the 6th Lake dam, is undertaking a project to rehabilitate the dam sometime after 2023 which may require a more significant drawdown thus exposing more of the invasive plants and increasing the annual die off.

On July 11th, the Association Board met with Dan Kelting, who is the Executive Director of AWI and one of the principal authors of our report.  The meeting was extremely helpful in putting these findings into context and developing a long term mitigation strategy.  Our options really fall into one of three categories, including:

  1. Intensive Whole Lake Control, which will reduce (not eliminate) invasive plants to a “maintenance level” where the incidence of invasive plants is reduced to rare (<5%).  AWI estimates this will require 7 to 18 years at a cost ranging from roughly $300,000 to $600,000 plus future annual maintenance costs.
  • Localized Control, which would target problem areas and can be done more affordably and at whatever pace we choose.  The simplest option here would be the use of benthic barriers that are essentially sheets of plastic weighted down on the lakebed that smothers aquatic plants.  This would only be done in areas where the plant life is dominated by invasive species such as the 6th Lake outlet area.  Also, this work could be DIY using membership volunteers.  Another localized option is hiring professional divers to hand harvest invasive plants.  This work was actually done in the past on our lakes and has proven to be helpful.
  • No Further Action, which would include maintaining status quo including boat launch monitoring, annual drawdown, and other passive stewardship activities. 

We do not believe the Whole Lake Control option is financially viable nor do we see the incremental benefit we would receive from such an expenditure of time and money.  Likewise, we do not believe doing nothing is the right thing either even though the situation does seem to be stable.  Rather, we are recommending an approach that seeks to maximize the possible benefit we may get from the dam rehabilitation project, and then follow that with ongoing localized control activities in targeted areas. 

Specific actions include:

  1. Obtain a mitigation permit from the Adirondack Park Agency which allows us to conduct future control actions.
  2. Maintain the boat steward program at the 7th Lake boat launch.
  3. Continue to solicit membership funding specific to invasive species control in anticipation of future costs.  Currently, $30 per year is asked from each member family.
  4. Investigate other sources of public funding e.g., grants, member items.
  5. Monitor the 6th Lake dam rehabilitation project, and seek to influence timing and drawdown actions to maximize invasive plant control.
  6. Once we better understand what will happen with the dam project, develop and undertake localized control options including benthic barriers and underwater hand harvesting starting with the area near the dam.
  7. Resurvey the lakes sometime between 2025 and 2030.

Respectfully submitted,

Board of Directors, 6th and 7th Lake Improvement Association