Ponds and lakes go through a natural aging process, and considering the “goal” of the erosion process is to fill in low areas with eroded earth from tall areas, the progression eventually fills in the pond or lake. In other words, nature’s goal is to turn your pond into land. Also, each pond or lake has several segments or zones.
Ponds or lakes are divided into 3 categories; they are either Oligotrophic, Mesotrophic, or Eutrophic stages of their life (listed youngest to oldest).
Oligotrophic bodies of water are considered new or young ponds or lakes in the overall scheme of things. Oligotrophic ponds and lakes have a low concentration of nutrients, such as nitrogen and phosphorus. They typically have steep sloping shorelines and are deep and clear. The bottom of the pond or lake is typically sand, gravel, or rock. Since oligotrophic lakes have little nutrients in them, they do not produce an abundance of aquatic plants and algae; therefore, they do not need as much treatment for water quality problems.
Mesotrophic bodies of water are considered middle aged, geologically. Mesotrophic lakes fall in the middle, between oligotrophic and eutrophic lakes. They have more nutrients and, therefore, more plant and algae growth than oligotrophic lakes and pond, but less than eutrophic. As a pond or lake ages from oligotrophic to mesotrophic, the sides of the pond begin to slope less and the bottom of the pond begins to fill in with organic material. The substrate that was once rock, sand, or gravel, now consists of mud on top of the rocks. Since Mesotrophic lakes have enough nutrients to produce plants and algae, they are in need of some treatment to slow down the aging process.
Eutrophic bodies of water are considered old or dying ponds or lakes. Eutrophic lakes and ponds are extremely well nourished with nitrogen and phosphorus, leading to an abundance of aquatic plant growth. As the pond or lake continues to age, the sides continue to flatten out and what were once steep sides is now gently sloping. The bottom of the pond is now filled with organic sediment and mud. The overall depth of the pond or lake is continually decreasing and the clarity continues to decrease. As the pond or lake fills in and the weeds grow larger, the total open water area shrinks as well. If left alone, the pond or lake will eventually fill in completely, and become a swamp or wetland at best. Most existing farm ponds fall in the eutrophic category and need help quickly to slow the aging process.