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.