Changes in nutrient concentration are reflected in changes in plant populations. Planktonic algae and benthic plants are in direct competition. An increase in one componenet usually is accompanied by a decline in the population of the other. Continuous fertilization with N and P above the level of .05 mg N/l and .005 mg P/l leads to a dominance in the summer phytoplankton population. A cessation of enrichment causes the plant population to return to natural levels. The concentrations of P-PO4 remain high and it appears that nitrogen is the more limiting of the two elements under natural conditions. Prolonging the cover of the ice has the same consequence as adding additional nitrogen to the water. Although aquatic environments can recover rapidly from enrichment and re-establish near normal vegetation conditions, they are liable to be easily disturbed by unusual natural occurrences such as prolonged ice cover due to exceptionally cold winters.