Lake Restoration

Plans To Restore Lake Mamanasco

An exhaustive study of the lake and its watershed, completed in 1990, recommended a two-pronged management approach for the restoration and preservation of Lake Mamanasco. The first action was to implement an effective watershed management program with a goal to reduce the nutrients entering the lake from the watershed. The second was to take steps to control or manage the problem of excessive aquatic weed growth until the lake naturally adjusts to the lowered pollution levels. This would be accomplished through lake management techniques such as chemical application and/or winter drawdown.

In 1997, the Mamanasco Lake Improvement Fund (MLIF) instituted a ten-year program for the restoration and preservation of Lake Mamanasco. The long-term goal of the plan is to reduce the phosphorus entering the lake from the watershed. The short-term goal is to control aquatic weed and algae growth so as to maintain the lake as a viable community and recreational resource through effective lake management measures. The methods being employed to accomplish these goals are as follows:

Watershed Management

More than 300 kilograms of phosphorus enter the lake each year from the watershed. Fifty percent of that amount comes from stormwater input, 24% from groundwater seepage, 16% from the lakes two main tributaries, and the rest from birds and atmospheric deposition.

1. Plans to limit the phosphorus entering the lake from stormwater runoff:

In 1996 Land-Tech Consultants Inc. was commissioned by MLIF to develop a watershed management plan for Lake Mamanasco. The objectives of this project were to assess current watershed conditions, identify non-point source pollutants, (i.e., polutants whose source is

not readily discernable), and design and develop a stormwater and sediment management plan for the drainage area on the western side of the lake.

In Phase I of the study, the watershed was divided into grids and prioritized based on existing or potential sources of non-point source pollutants. For the seven highest priority grids, accepted best-management practices (BMP’s) were evaluated and then chosen based on their effectiveness, initial cost, cost to maintain, and freedom of access. Phase II of the study consists primarily of surveying and engineering design. The work will be done over a five-year period to spread out the cost. Phase I of the study, which was paid for by a $15,000 community grant from the Town of Ridgefield, has been completed. Work on Phase II for Priority Grid I is underway, being partially funded by MLIF and a $12,000 grant from the town.

The study will address the inadequacy of the public infrastructure in the watershed, i.e roads, catchbasins, drainage facilities, etc., as well as drainage problems occurring on private lands. When the construction defined in the engineering study is completed, a 50% reduction of phosphorus from stormwater sources is anticipated.

2. Plans to limit the phosphorus entering the lake from groundwater seepage:

The 1990 Baystate study and a study done in 1981 by the Environmental Review Team (ERT) identified the source of contaminated groundwater to be primarily as a result of failing septic systems in the watershed. The ERT study also recommended that, “A study be undertaken to determine the options and costs associated with providing an alternative means of sewage disposal.”

In-Lake Management Techniques

1. Chemical Treatments:

In 2004, the lake was treated twice for algae with copper sulfate.

In 2005, there will be a Sonar (Flouridone) treatment to combat a reappearing infestation of Eurasian Watermilfoil. Although, this is not a preferred long-term method for weed control since it adds to the lake’s biomass, which eventually becomes another source of nutrients, it is the only effective short-term means available to control the aquatic weed growth.

Application of Sonar by Lycott Environmental Inc.
2. Winter Drawdown:

In other lakes and reservoirs, this technique has proven effective as a means of weed control. One of the benefits of a drawdown could be a significant compaction of bottom sediments which may increase the effective depth of the lake, thereby impeding future weed growth. An additional benefit is impeding growth in the exposed areas and to give lakefront property owners a chance to clean up the perimeter of the lake.

Since no draining device existed at the Mamanasco Dam, in 1996-1997 MLIF spent in excess of $10,000 to construct a siphoning system to facilitate the drawdown procedure.

Siphoning System Consisting of Six 8″ Pipes

A two-foot drawdown (we are not allowed to exceed this depth at this time) which exposed some of the bottom around the lake’s periphery, was completed in the winter of 2004-2005.

3. Egg Addling:

With the permission of the Connecticut DEP, MLIF has conducted a program of goose egg addling sine 1995, resulting in a significant decrease of resident geese. Geese feces are a source of bacteria, as well as the nutrients phosphorus and nitrogen.


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