Oligotrophic lakes are low in nutrients and primary production, rich in oxygen throughout, and have good water clarity. Dimictic lakes turn over twice a year, during the spring and the fall. This remixes dissolved oxygen and nutrients, needed by plants and animals in the lake. In the fall, the surface water becomes cooler and denser than the bottom waters. This cooler water sinks to the bottom, mixing the lake water. In the winter as temperatures drop further, ice forms on top of the lake and stops any further mixing. During the spring, the lake is heated by the sun and the cooler, less dense water floats to the top and the warmer, denser water extends to the bottom. As summer progresses, the temperature and density differences between upper and lower water layers become more distinct. These lakes generally become physically stratified into three identifiable layers in the summer and winter.
There are several thousand occurrences statewide. Many documented occurrences have good viability and are protected on public land or private conservation land. This community has statewide distribution, and includes several high quality examples. The current trend of this community is probably stable for occurrences on public land, or declining slightly elsewhere due to moderate threats related to lakeshore development, invasive species, and atmospheric deposition.
The number and acres of oligotrophic dimictic lakes in New York have probably remained stable in recent decades as a result of local lake protection efforts and state wetland protection regulations. Atmospheric deposition of pollutants (e.g., acid rain and heavy metals) may diminish oligotrophic dimictic lakes, especially in the Adirondack Mountains.
The number and acres of oligotrophic dimictic lakes in New York are probably comparable to historical numbers, but the water quality of several of these lakes has likely declined significantly as a result of several human caused disturbances (e.g., atmospheric deposition, impoundments, nutrient and pollution run-off, invasive species, watershed development, etc.)
Oligotrophic dimictic lakes are threatened by shoreline development and its associated run-off (e.g., residential, commercial, agricultural, and roads), recreational overuse (e.g., powerboats, intensive fish stocking and removal), and habitat alteration in the adjacent landscape (e.g., logging, pollution run-off, and increased impervious surfaces within the watershed). In addition, alteration to the natural hydrology (e.g., impoundments, dredging) and reduction in water quality (e.g., siltation, trash, turbidity, septic/nutrient run-off) are threats to oligotrophic dimictic lakes. Many lakes are threatened by the spread of non-native invasive species, such as Eurasian milfoil (Myriophyllum spicatum) and zebra mussel (Dreissena polymorpha). Atmospheric deposition of pollutants (e.g., acid rain and heavy metals) is a particular threat to some oligotrophic dimictic lakes, especially in the Adirondack Mountains (Jenkins et al. 2005). Although most lakes are recovering from historical DDT impacts, there is the potential threat that the proposed use of herbicides to control exotic plants (e.g., SONAR) may affect non-target native species.
Where practical, establish and maintain a lakeshore buffer to reduce storm-water, pollution, and nutrient run-off, while simultaneously capturing sediments before they reach the lake. Buffer width should take into account the erodibility of the surrounding soils, slope steepness, and current land use. If possible, minimize the number and size of impervious surfaces in the surrounding landscape. Avoid habitat alteration within the lake and surrounding landscape. For example, roads should not be routed through the lakeshore buffer area. If a lake must be crossed, then bridges and boardwalks are preferred over filling and culverts. Restore lakes that have been affected by unnatural disturbance (e.g., remove obsolete impoundments and ditches in order to restore the natural hydrology). Prevent the spread of invasive exotic species into the lake through appropriate direct management, and by minimizing potential dispersal corridors.
When considering road construction and other development activities, minimize actions that will change what water carries and how water travels to this lake community, both on the surface and underground. Water traveling over-the-ground as run-off usually carries an abundance of silt, clay, and other particulates during (and often after) a construction project. While still suspended in the water, these particulates make it difficult for aquatic animals to find food; after settling to the bottom of the lake, these particulates bury small plants and animals and alter the natural functions of the community in many other ways. Thus, road construction and development activities near this lake type should strive to minimize particulate-laden run-off into this community. Water traveling on the ground or seeping through the ground also carries dissolved minerals and chemicals. Road salt, for example, is becoming an increasing problem both to natural communities and as a contaminant in household wells. Fertilizers, detergents, and other chemicals that increase the nutrient levels in lakes cause algae blooms and eventually an oxygen-depleted environment where few animals can live. Herbicides and pesticides often travel far from where they are applied and have lasting effects on the quality of the natural community. So, road construction and other development activities should strive to consider: 1. how water moves through the ground, 2. the types of dissolved substances these development activities may release, and 3. how to minimize the potential for these dissolved substances to reach this natural community.
Survey for occurrences statewide to advance documentation and classification of oligotrophic dimictic lakes. A statewide review of oligotrophic dimictic lakes is desirable. Continue searching for large lakes in good condition (A- to AB-ranked). Review and incorporate data on occurrences gathered by partner organizations (e.g., Adirondack Lakes Survey Corporation).
There is a need to research the composition of oligotrophic dimictic lakes statewide in order to characterize variations. Continued research is needed on the impacts that atmospheric deposition has on this community.
Oligotrophic dimictic lakes are widespread throughout New York State, and are especially common in the Adirondack Mountains.
This broadly-defined community may be worldwide. Examples with the greatest biotic affinities to New York occurrences are suspected to span north to southern Canada, west to Minnesota, southwest to Indiana and Tennessee, and southeast to North Carolina.
Oligotrophic dimictic lake communities are the aquatic communities of nutrient-poor lakes that often occur in deep, steeply-banked basins. The lakes are dimictic, meaning they have two periods of mixing and turnover (spring and fall); they are stratified in the summer, then they freeze in winter and become inversely stratified. Common physical characteristics of oligotrophic lake communities include blue or green highly transparent water (Secchi disk depths from 4 to 8 m), low dissolved nutrients (especially nitrogen and calcium), low primary productivity, and sediment with low levels of organic matter. Additionally, the lakes have an epilimnion volume that is low relative to the hypolimnion, high dissolved oxygen levels year-round through all strata, and low alkalinity. The plant community is primarily in the shallow parts of the lake, between 1 and 3 m (3 to 10 feet), and is dominated by rosette-leaved aquatic species. Characteristic species include seven-angle pipewort (Eriocaulon aquaticum), water lobelia (Lobelia dortmanna), quillworts (Isoetes echinospora ssp. muricata, I. lacustris), milfoils (Myriophyllum alterniflorum, M. tenellum), bladderworts (Utricularia purpuea, U. resupinata), tape grass (Vallisneria americana), and creeping buttercup (Ranunculus repens). The zoological community of oligotrophic dimictic lakes are diverse, and include a variety fish and invertebrates, but in low abundances. In the shallow areas the characteristic fishes are warm water species, such as smallmouth bass (Micropterus dolomieui), redbreast sunfish (Lepomis auritus), pumpkinseed (L. gibbosus), rock trout (Ambloplites rupestris), and yellow perch (Perca flavescens). In the deeper waters, cold water species, such as lake trout (Salvelinus namaycush) and round whitefish (Prosopium cylindraceium) are common. Characteristic mollusks include freshwater mussels such as eastern lampmussel (Lampsilis radiata), eastern elliptio (Elliptio complanata), and eastern floater (Pyganodon cataracta), and snail species such as ramshorn snail (Heliosoma trivolvis), physid snail (Physa heterostropha), and amnicolas (Amnicola spp.). Other invertebrate species characteristic of oligotrophic dimictic lakes are midge larvae, such as Tanytarsus spp. and Procladious spp., caddisflies (order Trichoptera), and oligochaete worms (order Oligochaeta). A variety of phytoplankton and zooplankton species are present in oligotrophic dimictic lakes. Desmids (Staurastrum spp.), chrysophytes (Dinobryum spp.), and diatoms (Tabellaria, Cyclotella, Asterionella) are among the phytoplankton present, and rotifers (Phylum rotifera), copepods (Class Copepoda), and water fleas (Daphnia spp.) are often present in the zooplankton community.
A nutrient-poor lake within a deep, steeply-banked basin, with very clear water that is blue or green. Oligotrophic lakes have two cycles of mixing per year, and are characterized by low primary productivity, high dissolved oxygen, and low alkalinity. The plant community includes rosette-leaved species such as water lobelia (Lobelia dortmanna) and seven-angled pipewort (Eriocaulon septangulare), and floating aquatic species such as tape grass, milfoil, pondweed, and bladderwort.
Known examples of this community have been found at elevations between 128 feet and 1,468 feet.
The characteristic flora of oligotrophic dimictic lakes is at its peak in mid to late summer. Aquatic plant species such as water lobelia and bladderwort can be observed in bloom at this time.
Eriocaulon aquaticum (northern pipewort, northern hat-pins)
Isoëtes echinospora ssp. muricata
Lobelia dortmanna (water lobelia)
Elatine minima (lesser waterwort)
Myriophyllum alterniflorum (alternate-flowered water milfoil)
Myriophyllum tenellum (slender water milfoil)
Potamogeton gramineus (grass-leaved pondweed)
Potamogeton perfoliatus (clasping-leaved pondweed)
Potamogeton robbinsii (Robbins's pondweed, fern pondweed)
Ranunculus repens (creeping butter-cup, creeping crow-foot)
Utricularia purpurea (purple bladderwort)
Utricularia resupinata (reclined bladderwort)
Vallisneria americana (water-celery, tape-grass)
This figure helps visualize the structure and "look" or "feel" of a typical Oligotrophic Dimictic Lake. Each bar represents the amount of "coverage" for all the species growing at that height. Because layers overlap (shrubs may grow under trees, for example), the shaded regions can add up to more than 100%.
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This guide was authored by: Jennifer Garret
Information for this guide was last updated on: March 7, 2019
Please cite this page as:
New York Natural Heritage Program. 2019. Online Conservation Guide for Oligotrophic dimictic lake. Available from: https://guides.nynhp.org/oligotrophic-dimictic-lake/. Accessed July 16, 2019.