Restoration goals for urban lakes

For us to enjoy the lakes spread across our towns and cities, all its components should work well, including the water quality.

How do we know when the water quality of a lake is good or bad? Well, it is easier to say when it is bad. There would be floating waste or slimy scum on the surface of the water and an offensive smell emanating from the lake. The water would appear dark (black, brown or green), and there may not be a lot of different bird species seen or plants growing in and around it.

But when it comes to knowing if a lake is good, we may have multiple qualifications like the lake does not smell, the colour of the water is lighter and we can see a little inside the lake. Or the lake has a wide range of birds and plants. It is better maintained, with comfortable walkways for people, parks for children to play, or benches for visitors to sit among nature. The reasons may differ for different people. However, they are all important to determine whether a lake is good. But our study focuses on water quality, a major component having a wide-ranging impact on the overall lake.

To change the quality of water in a lake from bad to good, we need to take up some work or repairs. These are referred to as the restoration work of a lake. To restore or fix the lake’s bad water quality, certain goals have to be set, and then steps have to be taken to achieve them. What could be these goals?

As a starting point, we have some criteria (see Table 1) set up by the Central Pollution Control Board (CPCB) for surface water bodies (such as rivers and lakes) for different water-related uses.

Presently, the main trend for water quality monitoring is to go to a water body like a lake, collect sample(s) and then test the water for the parameters mentioned in Table 1. Based on the test results, a category is assigned, and the lake is designated for that use. But such an approach has an issue as it does not cater to the needs of the people living around the lake or dependent on it for economic support (such as fishermen). The category-based assigned use might not be even relevant for the lake in its given surrounding. In such cases, what could be the alternative? One approach could be to ask the local people and those economically dependent on the lake about the uses that they derive from the lake and if these uses are being met at a satisfactory level. This exercise could be carried out on a large scale across many lakes so that a broad picture can be drawn as to the various lake uses and the ranges of water quality that support these uses. But why do we need a range of water quality for these uses?

Lakes are dynamic, in that they are natural systems even if they are artificially created. Given that the lakes in Bengaluru are interconnected, there are no fixed numbers that can be meaningfully assigned to these uses. Instead, what would be useful is to have a range that defines the space within which the uses are supported and beyond which the uses are reduced or negatively impacted.

So, in order to start restoring lakes that have bad water quality, it would be beneficial to set water quality goals supporting the different uses as stated by people dependent on the lake and regularly interacting with the lake for indirect benefits.

Restoration work tends to be after a lake’s condition goes bad. While such work is important, restoration work should also be pre-emptive and try to ensure the multiple uses are supported post-restoration. Restoration goals should be aligned with what best helps support the different lake uses on a long-term basis. This might require the concerned authorities to revisit and analyse what steps need to be carried out and to what extent. Not all goals require all the restoration processes, and not all lakes need the same amount of restoration work.

Goals need to be dynamic for a city like Bengaluru that is ever-changing. Along with tools to adapt these goals, there should be tools and methods to track the changes or the condition of the lake water quality over time.

One of the standard methods involves collecting water samples and having them tested in laboratories. While this method yields accurate results, it is a skilled task, labour-intensive and expensive, and there are limited resources to carry out such work. An alternative method, which can be done by almost anyone, would be to observe and record the changes in the biological components of the lake, such as birds and plants (especially the plants growing along the shoreline and in/on the water). By tracking the different types of birds and plants seen at the lake and their numbers over time, we can observe how the occupants at the lake behave across seasons and if there is any sudden or gradual change in their presence. This will also help to understand whether the restoration work is fulfilling its goals or if any changes or interventions are required.