A Natural History of the Lake

By Sam Lee, RBL Dam Custodian

Just 80 years ago, a hiker walking through our neighborhood would have seen a wooded valley with streams running through it. Then, in 1936, an enterprising real estate developer built a dam and began to sell lots around the newly formed lake.  This is a brief history of our lake, concentrating on the lake itself rather than the community around it. 

It is important to understand that, unlike a natural lake, where water quality might start out pristine and become degraded with development, water quality of this man-made lake did not start out well. In 1947 the New York State Department of Environmental Conservation performed a site visit and concluded, “This lake, by virtue of its artificial origin, has definite undesirable characteristics… it is quite apparent that, at this time, it is not suitable for any variety of freshwater fish.” The negative report cited high biological oxygen demand, high dissolved CO2, and unfavorable acidity levels. The reported also mentioned high sulfur dioxide content due to the improper clearing of trees and vegetation prior to damming. The stumps, still visible poking up from the lake floor, are our reminder of the wetland forest that was.

Good water quality or not, people like to live near a lake. Property was sold, homes were built. In 1954, with the buildable lots remaining in private hands, the lake itself (and some of the unbuildable surrounding land) was transferred to the town of Putnam Valley as the RBL Improvement District. The stated goals were to enhance property values, offer new recreational opportunities, and support the biological and physiochemical processes of the lake ecology.

In 1969, the US Geological Survey conducted the next major ecological study of RBL. That study described three problems: ice damage to shoreline property, black fly and mosquito breeding grounds, and too many aquatic weeds. Pesticides and herbicides were applied and a four-foot draw-down was performed. The 1969 survey noted that the lake did not host much diversity of either aquatic plants or animals. The lake was, however, supporting fish – small sunfish and bass. 

In 1990, Dr. Robert Kortmann of Ecosystem Consulting Service (ECS) conducted the first large comprehensive study of RBL. The 1990 study included bathymetry (basically a map of the lake bottom, including water column depths), along with measures of internal nutrients, watershed nutrients, and plant and animal populations. The flushing rate was determined to be 1.29/year, which means that, on average, the entire volume of water in RBL is replaced every 283 days. 

Bladderwort was listed as the predominant aquatic plant nuisance, with Eurasian milfoil (an invasive aquatic plant) and coontail ranked below. (We note that residents today still consider bladderwort and Eurasion milfoil to be quite a nuisance.)

In his lake management plan, Kotmann identified the big problem as accelerated eutrophication.  Accelerated eutrophication describes a situation in which elevated levels of nutrients—nitrogen and phosphorus—encourage overgrowth of water plants and algae, which eventually decompose and use up the oxygen in the lake.  The result is an environment where fish, other animals, and many plants suffocate and cyanobacteria (toxic algae) thrive.  Some of the high nutrient levels in our lake at the time were due to the disturbances of development and the vegetation in the lake dying off quickly each fall. However, the report also identified a newer, bigger problem: “substantial septic related load.” 

The 1990 study warned against increasing development in the watershed. More home construction and expansion would contribute to more nutrient runoff and sedimentation into the lake. The investigators postulated that more runoff, more sand from beaches, and more decomposing plants could adversely affect the largemouth bass nesting habitat, lead to smaller bass, and allow sunfish to become the dominant species in the lake.

The study offered five recommendations: 1) Localized retention basins, 2) Preservation of wetlands, 3) Use of greenbelts and vegetative buffer areas, 4) Implementation and enforcement of soil erosion control and ordinances, and 5) Sound land use planning 

In 2007, Dr. George Knocklein conducted a second aquatic weed study at RBL. It showed 55 acres to have dense surface reaching plants, including fanwort and curly-leaved pondweed, two invasive species not previously identified in the lake. In 2010, RBL began participating in the state’s Citizen’s Statewide Lake Association Program (CSLAP), in which resident volunteers take water samples 8 times each summer.  Resident Bill Brigham personally sampled our lake water 40 times from 2010 to 2015.  The program continues today, under Sam Lee and Ina Cholst.  The work of our volunteers and the generous support of NY State, gives us a critical set of week-to-week and year-to-year data, including nutrient levels, chlorophyll levels and clarity. Altogether, the CSLAP data is invaluable, providing us with baseline and ongoing measurements of the concentrations of nutrients and contaminants and objective measurements of clarity and algae growth in our lake.

Lake drawdowns have been a source of concern for some residents. In the past 6 or 7 years, we have had at least 3 deep drawdowns in excess of 6 feet for beach and dam maintenance projects. Some residents have said that is too much, and are concerned about the lake levels coming back to normal each spring.

In 2012, concerned about lake weeds impeding boating and swimming in the lake, residents considered sterile grass carp as a means to address the problem. A series of public district meetings were held with NYSDEC Fisheries Biologist Michael Flaherty. Both Flaherty and the NYS Aquatic Plant Biologist Scott Kishbaugh found no reasons to object to the stocking of sterile carp into RBL, based on the objective data collected on the lake over its history. In 2012, 500 sterile grass carp were introduced to RBL (based upon a stocking rate of 6 fish per vegetated acre). The aim was never to eliminate aquatic plants – the plants help oxygenate the water, absorb nutrients, and support the fish population. The aim was to keep the plants at a level where residents could swim, boat, and fish comfortably in the lake. 

The sterile grass carp have been intermittently successful in controlling aquatic weeds. Use of the lake for boating and swimming has somewhat  improved. However, algae may thrive when their plant competitors are reduced. Therefore, we are keeping close track of the lake’s clarity and algal growth, especially toxic algae.

Ultimately, though, to successfully control both nuisance lake weed and algae problems, we will have to control the nutrients that are going into the lake (from septic systems, sediment run-off, and fertilizers, among other things). 

For many similar lakes (Oscawana and Peekskill, for example) septic systems have been shown to contribute approximately 50% of the nutrients (phosphorus and nitrogen) going into the lake. In the fall of 2016, Town Supervisor Sam Oliverio conducted surveys and held a series of public meetings to assess public support for more stringent septic maintenance in the Roaring Brook Lake District. With community approval, the Town Board passed a septic pump-out rule requiring pumping every 5 years. Neighbors rose to the occasion and we saw septic pumping trucks on the roads in unprecedented numbers in 2017.

Also in 2016, Supervisor Oliverio and the Town Board approved budgeting for the first full set of lake assessment studies to be done in Roaring Brook Lake since 1991 and the preparation of a comprehensive Lake Management Plan for the lake. 

Let’s look at where we are now. Our first stage in the reevaluation of the lake began in 2016 with a detailed updated study of the lake’s plants and vegetation.  A new bathymetry study was done in the spring of 2017. This lake-bottom mapping can be compared to the 1991 study, done 26 years ago, and helps to identify sedimentation hotspots, such as the coves, that are becoming clogged with mud. This information can help us plan and fund potential future projects to mitigate the current damage and reduce future runoff damage. 

It is too early to tell, but it appears likely that the lake will benefit from the 2016 RBL District law requiring all septic tanks to be pumped and inspected at least once every five years. (We note here that residents on the lakefront or with older septic systems should ideally pump their tanks every 2-3 years). In addition, we hope that we can begin to gradually substitute newer, more effective technology septic systems for some of the more outdated systems around the lake. We will be exploring creative ways to fund updating of septic systems for homeowners who wish to make those changes.

Now is always the time to make plans for long-term steps to protect the lake environment. Town Supervisor Sam Oliverio, the RBLPOA, and the community all support setting aside a fund for active protective lake management, under the ongoing direction of a professional lake manager. It is better—and more sustainable—to stay on top of lake problems year to year than to wait until there is an emergency that requires a huge budget response.  

We see the probable strategies today as being not much different than those identified in 1991 (except possibly adding more effective advanced technology septic system management, not available in 1991.

If our community had moved on some of these recommendations more decisively in the 1990s, we might not have reason to be as concerned as we are now, 30 years later. We all know that our use and enjoyment of the lake, as well as the property values of our homes, depend on our care of the lake. Though we understand more now about ecology, we have basically the same goals as the people who created the lake and set up the tax district all those years ago: 

“To enhance the property value and recreational opportunities, and support the biological and physiochemical processes associated with the organic evolution of this man-made impoundment known as Roaring Brook Lake.”