Not to scale, fortunately!
The oligotrophic lake is clear, rich in oxygen and has certain characteristic algae, insects, fish and other life. The abundance of such fishes as trout, salmon and smallmouth bass is a good indication of an oligotrophic lake. This lake form also has lots of oxy gen on its bottom and shows no decline in oxygen levels in comparison with the waters above. For this reason, organic matter does not last too long here. For use by man, the waters of an oligotrophic lake are most desirable.
On the other hand, a eutrophic lake is very productive with its own characteristic algae, insects, fish, etc.. There are many algae blooms in summer which may create some cloudy water. Fish abound in a eutrophic lake; the most common types are largemouth bass, sunfish and pike, among other species. Whereas the major aquatic insect representatives of an oligotrophic environment are the mayflies and stoneflies, those of a eutrophic lake are such beasties as diving beetles, water bugs and dragon fly nymphs. The productive lake also shows a significant decline of oxygen content in the water, especially at the bottom. This is due to the amounts of organic matter generated in and around t he lake which settle to the bottom, and then consume the oxygen in the process of decomposition. High class fish like the lake trout cannot survive here because of the lower levels of dissolved oxygen in the water.
The dystrophic lake phase occurs when there are high levels of nutrients in the water and when so much organic matter is being produced in and around the water that only partial decomposition occurs on the bottom of the lake forming what is known as pe at. These lakes also have their own characteristic algae, insects and fish. Low oxygen tolerant organisms such as carp, mud minnows, dragon flies and giant water bugs replace their predecessors of the eutrophic lake. There are also quantities of emergent vegetation, especially around the edges of the lake. At this stage, there is zero oxygen on the deep bottom of the lake, thus no fish can survive. Aerobic life exists only in the shallows of a dystrophic lake during summer.
Seneca and Cayuga Lakes, although well aged chronologically, are ecologically in good shape. During the last ten thousand years each lake has accumulated over five hundred feet of sediment on its bottom. This represents less than 0.5 inches per year if the lakes were to fill straight up on the vertical. Nevertheless, with the abundance of oxygen, trout, mayflies and the like, the lakes are very strongly symptomatic of oligotrophy and should remain such for more than 11,000 more years.
However, heat and nutrients, such as phosphates, accelerate the rate of eutrophication of a lake. The Lake Source Cooling project proposed by Cornell will redistribute phosphorus to an area of the lake where the nutrients can support plant life, effectively increasing the phosphate content, but not actually adding additional phosphates. The project will also directly add heat to the lake.
CLDF 1998