Science

Getting to the Bottom of Things: Why Are Some Lakes Mucky?

Driving around our great state, you are likely to see a wide range of scenery out your window. Forests, hay fields, wetlands, rivers, bogs, meadows, granite outcrops, orchards, and sub-alpine terrain all dot the landscape of Vermont. Just as there are many types of landscapes, Vermont has many types of lakes and ponds. From the giant (Lake Memphremagog, Newport) to the tiny (Tiny Pond, Ludlow), from the shallow (Lily Pond, Poultney) to the deep (Lake Willoughby, Westmore), no two lakes and ponds are alike. The Lakes and Ponds Program works with each lake community to assess a lake’s unique nature and determine how best to protect the lake and its watershed.

When people think of lakes, they may picture wading into crystal clear water from a sandy beach. But this picture doesn’t represent the reality of the diverse lake ecosystems throughout Vermont, where naturally sandy lake bottoms are rare. The diversity of lakes and ponds, including whether a lake has a sandy or a “mucky” bottom, can be attributed in part to how a lake formed as well as where it is located within the surrounding landscape.

Vermont’s deepest lakes were formed by glaciers gouging the earth, creating deep depressions that filled with water as the glaciers receded north and meltwater deposited boulders, sand, and gravel. Other lakes were formed in natural depressions from the creation of dams by the deposition of glacial material. In more recent times, humans have dammed natural lakes to artificially expand them and created artificial lakes by damming wetlands and rivers. These artificially expanded or created lakes and reservoirs are generally used for drinking water, hydroelectric power, or recreation. Some lakes were formed over nutrient-rich soils, while others were formed over bedrock. These formation characteristics drive many aspects of the lake’s current natural ecology, including the depth of the lake, whether a lake has a rocky, sandy, or mucky bottom, the types and abundance of aquatic vegetation, and the species of fish the lake supports.

20181203 Runnemede

Lake Runnemede in Windsor is an artificially created lake.

20181203 Little-Elmore-Pond

Little Elmore Pond in Elmore is considered a naturally formed lake.

Lakes are living, dynamic systems that are constantly undergoing slow successional change punctuated by more rapid changes in response to activities in their watersheds. Erosion from flood events and stormwater runoff deposits sediment into lake basins. Dying and decomposing aquatic plants and algae sink to the lake bottom to combine with lake bottom sediment. The accumulation of these sediments along the lake bottom is a natural process. Like all living systems, lakes age – even the largest and deepest lakes slowly disappear as their basins fill with sediment and decomposing plant material. Eventually, all lakes become wetlands or marshes. The natural process by which lakes form, evolve, and disappear takes thousands of years. Human activities along the shoreland and elsewhere in the watershed can change these lakes on much faster time scales.

Vermont encourages the protection and management of its public waters as complex ecosystems that age naturally. The Lakes and Ponds Program gets inquiries each year from lakeshore residents interested in altering mucky lake bottoms. Some lakeshore property owners request to add sand to the lakebed to create an artificial beach area while others seek to remove muck. It’s important to understand that mucky lakebeds are a natural feature of Vermont’s lakes and ponds attributed to how the lake was formed geologically and the age of the lake. Activities on the shoreland and within the watershed generating runoff can also contribute to the lake bottom characteristics. Placing sand or excavating the lakebed are activities that generally cannot be authorized under State regulations. Over time, added sand will wash away and be deposited to other places in the lake, contributing to additional sedimentation in the lake, and potentially blocking boat passage. Additionally, sand smothers benthic (bottom-dwelling) organisms that are important to the lake food web. Removing lake bottom sediments disrupts important shallow water habitat areas and organic sediments will likely return to any areas that have been excavated. A mucky area will never permanently convert to a sandy area.

There is much to celebrate about the diversity of lakes found throughout the state. Mucky lake bottoms provide excellent habitat for aquatic plants that in turn provide habitat for spawning fish, nesting areas for birds, rearing sites for young fish and wildlife, and shoreline protection from wave and ice action. Canoeing, kayaking, fishing, and bird-watching are all immensely enjoyable on shallow, muck-bottomed ponds, as they are generally teeming with wildlife. Many people embrace that squishy feeling between their toes as a chance to experience what makes Vermont’s lakes unique and worth protecting.