Encroachment is when construction activities affect natural areas including lakes and forests. It is very common across the country when laws are violated.
Encroachment can cause multiple problems:
Bottleneck for flowing water
Can cause flooding
Decrease in water clarity
Increase in phosphorus loading
Increase in algae growth
Affects fishes and other animals
Decrease in water runoff
Encroachment is the leading cause endangering lakes. It is quoted that over 80% of the lakes in Bangalore are endangered and a conservative figure of 60% would still be harmful to the people.
2. Contaminated Lake
Lakes have multiple inlets by design. Contaminated lakes have excess physical, chemical or biological pollutants in them.
Physical pollutants: garbage disposal, waste from cultural practices, plastics and metals.
Organic: Biomass, human compounds, pesticides, deceased organisms.
Inorganic: calcium, magnesium, sodium, potassium, carbon, chlorine, and sulphur
Plant Nutrients: nitrogen, silicon, and phosphorus
These have lasting impact on water-bodies:
Organic Compounds - Increase the aerobic bacteria and reduce anaerobic bacteria. Rich organic compounds also facilitate the growth of water plants like water hyacinth, water alligator and water lettuce among the others. That reduces dissolved oxygen content affecting fishes and tadpoles.
Inorganic Compounds - They increase toxicity of water and may cause temperatures to rise. Most common outcome is when fishes die and float on top of water. Such water is not fit for consumption or for any human activities.
They contaminate the groundwater.
Most commonly lakes with industrial inlets and untreated sewage inflow have this problem. To solve this, lagoons are constructed to make sure such water does not flow into the lakes.
3. Dry Lakes/ Dead lakes
Dry lakes are lakes which have entirely lost all of its water retention capacity and as a result gone dry. There is more evaporation than recharge.
As a result, the bed is filled with grass or sludge all the way across, not allowing any water to enter from the ground into the lakes.
Dry lakes could emerge out of:
Excessive encroachment that blocks the upstream flow into the lake.
Lack of water inflow.
Excessive groundwater extraction.
Changes in the catchment area
Man made changes in the topography of the land
Desilting process affecting the base clay layer of the lake.
Such lakes are used for some other purpose. They become dump yards or may have human settlements. It's critical to revive these lakes for the people living around these areas.
4. Shallow Lakes
Shallow lakes are naturally occurring. Wetlands also come in this category. All lakes do not need to be deep.
They create a better ecosystem. When kept well and clean, these provide a lot of support to animals and the ecosystem. They provide a diverse green cover with a wide variety of plants. Animals may also use this for cooling off and drinking.
Shallow lakes are usually secluded from city life.
These water bodies need to be observed to be maintained. They are threatened from unsolicited waste disposal.
5. Stagnant Lakes
Stagnant lakes have no flow of living water. In these lakes, the presence of silt is very high. The lake beds are therefore not porous which stops ground water recharge. The water is thicker with higher viscosity due to lower evaporation.
These are the common types of lake that are characterized by the growth of water plants. When waters are still and lakes not maintained, water hyacinths and other water plants multiply very quickly. This is because lake beds are full of nutrients from sewage that allows these water plants to aspirate.
These water plants create a mesh like system within the water bodies not allowing the movement of fishes. Aquatic animals perish in such lakes.