Know Your Watershed I: [Images not yet added]

Overview of the Challenge

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Here is a snapshot of where we are (May 2024):

  1. We continue to lose the long battle for a healthy lake. Excess plant growth from phosphorus overloading remains the chief problem.
  2. Health problems in Chebacco Lake and its ponds reflects human impact throughout the watershed.
  3. The threat horizon is worsening every year on three fronts:
    • Climate change is generating more droughts (4 in the last 8 years) and more heavy rainfalls (and resulting runoff), stressing the system and reducing its capacity to slow and filter the flow of nutrients, sediment, and pollutants.
    • Warmer climate is also accelerating the geographic spread of invasive species, both terrestrial and aquatic.
    • Land development pressure on environmentally sensitive sites, like 133 Essex Street, threatens to worsen the flow of nutrients, sediment, and pollutants.
  4. As with the human body, there is a set of vital signs of general health for lakes (water clarity, dissolved oxygen, nutrient level, and levels of microscopic plants called phytoplankton). Warning signs of ill-health were found in water quality sampling done in May and July of 2023:
    • Water clarity: Moderately poor. Vital biological processes are inhibited by the low penetration of sunlight. Visibility in 2023 was just 4 four feet of depth compared to 7 feet in 1984.
    • Dissolved oxygen: In over half the lake (where the depth exceeds 10 feet), water at the lake bottom is virtually devoid of oxygen creating unhealthy “dead zones” and stimulating the release of phosphorus from the sediments.
    • Nutrient level: Extremely high levels of both phosphorus and nitrogen were detected; much higher than readings in 1984 and conducive to algae blooms.
    • Phytoplankton (levels of microscopic plants): Analysis of phytoplankton present in 2023 indicate that high water temperatures and nutrient levels give a competitive advantage to cyanobacteria (including hazardous varieties) over other benign phytoplankton groups.
    • Important note: A reliable diagnosis of lake health requires multiple years of sampling and analysis, which will continue if we can raise the funds required. That said, these 2023 results match conditions in similar shallow lakes in New England and are a call to action.
  5. Humans impact these health indicators in four important ways:
    • We add excessive amounts of phosphorus in the form of human urine (and pet waste) to the environment, throwing off the natural nutrient balance in the lake and ponds.
    • Our homes and roads create impervious and semi-impervious (lawns) surfaces that accelerate the flow of nutrients, sediment, and pollutants into the lake and ponds while reducing the capacity of remaining forests, soil, streams, and wetlands to filter and bind these elements.
    • Climate change continues to ratchet up environmental stress on lakes and ponds: more intense rainfall; longer and more frequent droughts; more algae blooms; less snow and ice, earlier melt; more species and habitat disruption; and invasive species expanding their geographic range.
    • Fortunately, human impact can also be positive. The Wetlands Protection Act, Title 5, and Stormwater Management regulations provide some state-level mitigation. Chebacco homeowners avoided phosphorus-based fertilizers and detergents long before they were banned in Massachusetts. For decades, the Lake Association has promoted landscaping best practices to “slow the flow.” Today, the risk is greater but so is our understanding. We Can Do This! Let’s live lake-smart individually and invest in the collective efforts needed to preserve a healthy watershed for our children and grandchildren.


Information is Power! Lake Living & Learning will provide a strong foundation for homeowners and lake lovers about the watershed, the ecology of the lake and ponds, and the opportunities to engage in small and large ways to preserve the health of the Chebacco Watershed.

Know Your Watershed I continues with a broad description of Chebacco Watershed focused on three key watershed concepts:

  1. Watershed: Life Follows Water’s Flow
  2. Lakes and Ponds are a Watershed’s Hotspots
  3. The Water Cycle is the Heart of a Watershed Ecosystem


  1. Watershed: Life Follows Water’s Flow

A watershed, also known as a drainage basin or catchment area, is the land area that drains water, sediment, and dissolved materials to a common outlet, such as a lake, river, or ocean. It acts like a funnel, collecting and channeling water to a central point.

The Chebacco Watershed is the drainage basin encompassing Chebacco Lake, Beck Pond, Round Pond, Gravelly Pond, Coy Pond, and a mile of Alewife Brook (to the Apple Street bridge). These water bodies comprise just 7% of the watershed’s 7.2 square miles (4,600 acres).

Human development comprises 11% of the watershed. Forested areas make up another 58%, and wetlands 17%.

The watershed includes portions of five communities: Essex (1,890 acres), Hamilton (1,613 acres), Manchester-by-the-Sea (658 acres), Wenham (329 acres), and Beverly (110 acres).

Water flows naturally (no manmade dams or barriers) at a very flat gradient from the lake through Alewife Brook for over a mile to the Apple Street bridge (the terminus of the Chebacco Watershed) and then continues at a steeper gradient into the Essex River and the vast estuary known as Essex Bay. Thus, the Chebacco Watershed is the upper reach, and the Essex Bay the lower reach, of the Essex River Watershed.

Essex Bay is a significant part of the Great Marsh, the largest continuous salt marsh in New England. A major ecological resource and birding area, alewife (river herring) run the river each spring to spawn before returning to the ocean.

  1. Lakes and Ponds are a Watershed’s Hotspots

Only a little more than 1.2 percent of all freshwater on earth is surface water. Lakes and ponds are crucial elements within watersheds, accumulating surface water within the basin and stimulating vibrant biological communities. Unfortunately, “healthy watersheds are uncommon” [EPA], particularly in areas that are urbanized, farmed, or mined. Furthermore, inland waters are closely linked to changes in terrestrial and atmospheric processes through the transport and storage of water, nutrients, contaminants, and energy.

Part of the joy of living near Chebacco Lake and its tributary ponds is the ever-changing display of the natural world. The ecological abundance we enjoy changes so rapidly that it often seems we experience “52 seasons per year” rather than four!

Diverse biological communities and habitats comprise a land-water synergy crucial to the resilience of watershed ecosystems. Yet in geological terms, Chebacco Lake and the ponds are little more than puddles – “shallow lakes” of the type most vulnerable to natural or human-driven change.

Chebacco Lake, for example, is 209 acres but averages just 9 feet of depth with a maximum depth of just 22 feet. (The three yellow flags on the bathymetric map indicate key locations for our lake monitoring.) At the deepest portions of the lake, there are pockets of sediment 15 to 25 feet thick.

  1. The Water Cycle is the Heart of a Watershed Ecosystem

Precipitation and snowmelt are the initial water inputs within a watershed, followed by migration (surface runoff and groundwater flow), evaporation (from surface water), transpiration (from trees and plants), and man-made withdrawal (via wells). Fluctuations in precipitation influence lake levels, water quality, and ecosystem dynamics.

Precipitation in the Boston area has averaged 43 inches per year over the past 30 years; in the recent decade, we experienced a low of 31 inches in 2022 to a high of 53 inches in 2018.

Average monthly precipitation falls within a relatively narrow range of 3.1 to 4.3 inches. We get rain, on average, every third day year around.

Natural ecosystems throughout the Chebacco Watershed are remarkably adept at utilizing the normal flows of energy, water, and nutrients that cycle through the system. Birds arrive in the spring when insects appear; alewife swim upstream when the water temperature reaches 50 degrees; and invisibly, microorganisms in the lake and ponds are constantly modulating their activity based on sunlight, nutrients, and temperature.

Relatively rapid flushing and replacement of the lake’s water volume occurs from March through May. During the summer and early fall months, the flushing rate drops dramatically and water quality may be adversely affected. (Salem State study)

Natural systems become stressed under atypical conditions, both drought and heavy rains. We had significant drought in 2016, 2017, 2020, and 2022. In 2023, we had a particularly wet year with 14 storms of 1” or more. (Meteorologists report that storms of 3 or more inches are increasingly common.)

One the one hand, droughts reduce water quality through the concentration of nutrients and pollutants, temperature stratification and oxygen depletion, and increased turbidity (poor water clarity). In addition, droughts disrupt food webs, alter habitat, reduce biodiversity, and disrupt water levels.

On the other hand, heavy rainfalls reduce water quality through flooding and rapid runoff, sedimentation/pollution, nutrient overloading, and altered water chemistry. In addition, heavy rainfalls, like drought, disrupt food webs, alter habitat, change species composition, and stimulate algae blooms.

The increasing frequency of droughts and heavy rainfall is likely to chip away at the resilience of the watershed ecosystems. Together, we need to vigilantly monitor the changes and respond with mitigation wherever possible.


Know Your Watershed II: How (Un)healthy is Our Lake? summarizes the warning signs revealed in our 2023 water sampling and describes key biological watershed concepts including the role of phosphorus in promoting excessive plant growth.

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