Pashan lake, the pride of Pune, is dying! Water hyacinth continues to invade the lake and pollution levels in the lake are high, threatening its once rich biodiversity. How did this happen?
The lake was once birders’ paradise
This 130-acre wetland with a catchment area of 40 square kilometres is one of the oldest man-made structures built to store water in the country. The lake was made by constructing a barrage on a small rivulet--the Ram Nadi that originates in Bavdhan area in Pune and flows through the city into the Mula river--and is surrounded by residential areas, industry and defence institutions.
The stored water was used to meet the water needs of the Governor’s estate during the colonial times and fulfilled the needs of the Pashan village later. The wetland played an important role in maintaining the stability of the water tables during dry and wet periods. The wetland gradually evolved into an ecosystem of its own with dense vegetation and rare aquatic plants and many migratory birds started visiting the lake for their feeding and temporary residence.
Threatened by urbanisation
The fast pace of development in the 1990s gradually started taking a toll on the ecosystem of the lake. Urbanisation and aggressive deforestation on nearby hills led to heavy siltation resulting in the decrease in the depth of the lake. This had a negative effect on the bird population and studies in the year 2000 found that birds preferring deep waters were replaced by those preferring shallow water. Indigenous varieties of fish in the water declined gradually.
There was an increase in the chloride and phosphate content of the lake water due to the pollution by sewage and industrial effluents. This led to an increase in birds such as Indian Pond Heron and Black Winged Stilts and fish such as Tilapia which favour polluted water.
Efforts to restore the lake begin
Considering the poor state of the lake, a restoration plan was made by the Pune Municipal Corporation (PMC) in collaboration with Naik Environment Research Institute (NERIL), Pune in 2008 under the Jawaharlal Nehru National Urban Renewal Mission (JNNURM) to change this situation of the lake. The restoration involved:
- Draining and desiltation of the lake where part of the silt was used to construct a 17-acre island on the lake. Ten acres of this island was partially submerged to provide a resting ground for birds preferring shallow waters while the rest was left to serve as an undisturbed breeding and feeding ground for birds.
- Construction of the 1250-metre-long walkway, 700-metre-long embankment along with fencing around the lake to prevent human interference.
- Planting of around 1200 indigenous, fruit-bearing trees and shrubs on the embankment along the lake for attracting terrestrial birds.
- Strengthening of the bund and the protection of the Ram Nadi at the downstream of the lake by building a four-km-long retaining wall from the spillway and treatment of the catchment of Ram Nadi in the upstream of the lake.
- An environmental interpretation centre for visitors and a nursery at the lake.
The Rs 16.6-crore restoration work was completed by 2013. Mangesh Dighe, the environment officer from the PMC, Pune says, “Our conservation efforts helped in securing the lake premises, stop eutrophication, rejuvenate and increase the water holding capacity of the lake. The earlier barren areas around the lake have now been replaced by thick forestation. We did not want to turn this place into a tourist attraction; we wanted people to stop crowding the place and disturbing the bird habitats. The basic idea was eco-restoration and turning it into a place for bird watchers and people interested in studying the lake’s ecosystem.”
The lake continues to suffer
Sadly though, two years following the restoration efforts by the PMC, the state of the lake is back to square one and its condition continues to worsen. The lake has been invaded by pistia and water hyacinth and there has been a significant decrease in the number of migratory birds visiting it. A recent Environmental Status Report (ESR) by the PMC shows that the water quality of the lake continues to deteriorate with high biochemical oxygen demand (BOD), chemical oxygen demand (COD) and lower dissolved oxygen (DO) levels.
Mangesh Dighe adds, “Of course, water quality issues have persisted following the restoration efforts made by the PMC. But this has to do with the increasing growth and urbanisation that has been happening in the villages located upstream of Ram Nadi that continuously deposit large amounts of sewage into the river that reaches the lake. Most of this sewage comes from areas that are outside the jurisdiction of the PMC. How we address this still remains a challenge.”
Flawed restoration efforts to blame
Experts, however, disagree and attribute this gradual deterioration of the lake to the PMC’s “flawed development plan” around the water body. Professor Sanjeev Nalawade, head of the geography department at Fergusson college, Pune and a regular visitor to the lake, says, “Although the lake needed desiltation since 2000, instead of deepening the middle part of the lake which was once naturally deep, the PMC desilted and deepened the surrounding areas too, destroying the shallow water habitats”.
Dr Revati, a botanist from Ecological Society, Pune, says, “The actions by the PMC not only destroyed the rare aquatic freshwater plants, which are now being replaced by pistia and water hyacinth, but it also destroyed the marshy areas, the natural transit zone between the soil and the water, created by the receding water levels of the lake, thus destroying all the valuable plant and animal species in the area.”
Some, like Nalawade, believe that though the idea of developing islands was good, locating the island very close to the shore was problematic. “During the summer months, when the water level goes down, the islands get connected to the shore, giving stray dogs easy access to them. They destroy the eggs and chicks of lapwings and terns who nest in these areas. These two islands should have been developed near the centre of the lake, at least 200-250 m away from the nearest bank,” he says.
Other interventions such as strengthening the bund have not helped either. Dr Revati says, “Increasing the height of the bund near the lake has stopped the natural flow of the lake which has now been turned into a stagnant pond. The flow of sewage into the lake has further deteriorated the quality of the lake water which was clear before. The restoration should have been first tried in a small area to see its effects on the ecosystem before it was done on such a large scale.”
Pune-based biodiversity researcher and ornithologist Dharmaraj Patil believes that the project made critical interventions that led to the destruction of the lake habitat. “One of the major interventions was installing a rock wall surrounding the lake in the name of lake stabilisation. This destroyed the muddy banks, an important habitat for wader birds like Common Sandpiper, Green Sandpiper, Wood Sandpiper, Pintail Snipe, Common Redshank, Little ringed Plover and many more, leading to their decline,” he says. He also points out other interventions such as desilting of the lake and creating islands to have negatively impacted the invertebrate life in the lake. “The tree plantations have attracted birds like fantails, flycatchers, orioles, mynas, etc which are forest birds and not wetland birds. To conserve the lake, one needs to attract aquatic or wetland birds at Pashan lake,” he adds.
Experts such as Dr Swati Gole from the Ecological Society, Pune, question the idea of development and beautification of the lake that has destroyed its natural habitats. “Pashan lake, a wetland, should have been developed as a wetland. Instead, crores were spent to beautify it and natural habitats got destroyed,” she says.
Nalawade recommends a few damage control measures like the removal of stony edges from the embankments and changes in the slopes of the embankments from steep to gentle, to save the lake. He also lists out more open areas, replacement of trees by shrubs, development of muddy areas, deepening the channel between the islands and the nearest shoreline, controlling of sewage from entering the Ram Nadi and more involvement of public to improve the current state of the lake.
Patil adds, “The project was highlighted as the best example of public-private partnership. However, there was no public hearing on the project and only selected experts were consulted before modifying the lake ecosystem. It is important that the project is reviewed. Having a vigilance committee to monitor such projects to increase accountability and make corrections at the right time are needed to avoid wastage of valuable resources in the future. The money spent on reviving the lake was public money and it is important that the people are informed. People should come forward and take a stand to protect and conserve such natural heritage sites in the future”.
With the PMC already planning its next project--the restoration and beautification of the Mutha river-- it remains to be seen if it has learned anything from the muddle created at Pashan lake!