I say that this pond was quite clean and pleasant for many years, perhaps a couple decades.
Many, if not most all ponds and lakes, behave in this fashion. Ponds are collection basins. What solids enter and those that grow in the pond stay there. There is no flusher for ponds. As they age the materials continue to accumulate and from that, nutrient enrichment of the pond increases to gradually grow more and more plant vegetation. As nutrification, also can be called eutrophication, increases,,,, plant growth increases and often diversity decreases until the pond produces plants as to what it now has. This process continues until the pond is full of dead materials and again becomes a swamp, wetland and then dry land. It is a natural process and is called aquatic succession.
Ecology lesson for today. Nutrificaiton or eutrophication is the gradual increase in the concentration of phosphorus, nitrogen and other plant nutrients in an aging aquatic ecosystem such as ponds and lakes. This can be accelerated by human influences. The excessive growth of algae and larger plants in eutrophic waters is accompanied by the generation of a large biomass of dead algae and submerged plants. These dead plants sink to the bottom of the water body where they are broken down by decomposers primarily bacteria, which consume lots of oxygen in the process. The over production results in over consumption of oxygen that leads to hypoxic conditions (loss of oxygen) in the water. The hypoxic conditions at the lower levels of the water body can spread to the entire water body and lead to the suffocation and eventual death of larger life forms such as fish.
Natural eutrophication refers to the excessive enrichment of water bodies via natural events. For example, the nutrients from the land can be deposited into a lake or a river. These water bodies become overly enriched with nutrients, enabling the excessive growth of algae and plants.
