Lakes are inland water bodies, small to moderately large in size, with their surface exposed to the atmosphere. Most lakes fill depressions below the zone of saturation in the surrounding soil and rock materials. Also most lakes have a surface area less than 100 square miles. The largest fresh water body Lake Superior in North America 31180 mile. The majority of the lakes are relatively shallow. Some large lakes have depths less than 100 ft. Lake Baikal of Russia is about 5000 ft at its deepest point.
Lake classification can be done in many ways. Lakes can be classified according to their degree of enrichment with nutrients and organic matter. These classification of lakes are given below.
Oligotrophic lakes are nutrient poor, have low levels of algae & organic matter, good transparency and abundant O2.
Eutrophic lakes are nutrients rich, lakes have high levels of algae and organic matter, poor transparency and are often oxygen depleted.
Mesotrophic lakes have intermediate nutrients, often have abundant fish life thus have both elevated levels of organic matter production and adequate supplies of oxygen.
The process of nutrient enrichment of a water body, with increases with in organic matter is termed as eutrophication. This is considered to be natural aging process in lakes, part of succession of newly formed water bodies to dry land.