Fish choke to death in Jakkur lake

Several fish were found dead at Jakkur lake in North Bengaluru, allegedly due to entry of sewage along with rainwater after the recent rains in the city.

• For the last couple of days, the fish in the lakes are dying as a result of the polluted water. Locals are noticing fish dying over the last couple of days and the stench around the lake has become unbearable.
• As urbanization gathered momentum, since the 1990s, changes in land-use pattern combined with encroachments, domestic sewage, garbage, and effluent discharge has taken a toll on the scenic freshwater lake until it slowly turned into a dump for the city’s waste.

Jakkur Lake:

• Jakkur Lake is on approximately 160 acres and is located in the Northern part of Bangalore. The lake falls within Hebbal Valley as part of the Yellamallappa Chetty lake series in northern Bangalore.
• A 7-acre constructed wetland in the north of the lake has mostly been left to grow naturally. This wetland accounts for approximately 4.4% of the total lake area.
• There is a bund created with an outlet into the lake. There are species of plants in the wetland such as Typha, Alligator weed, and Water Hyacinth.
• It is observed that the growth of Hyacinth increases when the inflow of sewage water increases.

The reason behind the deaths of Fish:

• Aquatic organisms need dissolved oxygen (DO) to respire. It is necessary for aquatic animals, other microorganisms, and underwater plants. Dissolved Oxygen is defined as the amount of gaseous oxygen dissolved in the water.
• The chemical sewage contains a raw material that is utilized by aquatic plants and algae for their development and thus they increase in number which blocks the penetration of sunlight.
• As the aquatic plants and algae are increased in amount, the level of dissolved oxygen decreases which in turn creates a lack of oxygen availability and that affects the fishes and other aquatic organisms and may kill them as they uptake the oxygen from water.
• Due to the waste present in the water, the microorganisms present in the sewage consume all the dissolved oxygen, thereby depriving the fishes of the dissolved oxygen, and ultimately fishes die due to lack of availability of oxygen.

Additional Reasons/Information:

• Microbial activity increases Biological Oxygen Demand (BOD). BOD is the amount of dissolved oxygen needed by bacteria in decomposing the organic wastes present in water. It is expressed in milligrams of oxygen per litre of water. The higher value of BOD indicates a low DO content of water.
• When there is high turbidity in the water body then it can lead to the clogging of the gills of fishes and then their death.
• Eutrophication can also cause the death of fish. It increases the presence of an algae bloom and that can lead to oxygen depletion, resulting in the deaths of aquatic organisms.

Eutrophication refers to the addition of artificial or non-artificial substances, such as nitrates and phosphates, through fertilizers or sewage, to a freshwater system. It can be anthropogenic or natural. It leads to an increase in the primary productivity of the water body or “bloom” of phytoplankton.

• If there is an increase in sulfur dioxide level in the water body, then it has the potential of killing fish.
• Keeping sewage out or only releasing it into water bodies after undergoing treatment and routine harvesting of the wetlands are the possible measures that can be put to use to avoid such happenings in the future.