Explanation : Standing bodies of fresh water are often
divided into categories that reflect levels
of biological production. On the basis of
biological production the water bodies are
divided into Oligotrophic lakes, Eutrophic
lakes and Mesotrophic lakes.
Oligotrophic lakes are those that are
unproductive: net primary production is only
between 50 and 100 milligrams of carbon per
square metre per day, nutrients are in poor
supply, and secondary production is depressed.