Pilot 1: Water Pollution

Comprehensive monitoring of water pollution in small urban lakes

Berlin’s small lakes are ecologically critical hotspots, yet they face increasing climatic and urban pressure. The lack of information about their condition hinders management tasks. To address this gap, AD4GD has developed water quality and availability indicators by integrating IoT sensor data with satellite observations and citizen science contributions. These insights are made accessible through the Splashboard interface, enabling more informed and effective decision-making at the local level.

Lietzensee lake in Berlin. Image: Chris Danneffel (CC BY 3.0)

Berlin is considered to be a “green city”. 30% of its total area is covered by forests and other green spaces. 6% is covered by water. The latter comprises not only the Spree-Havel river and lake system, but also more than 300 small lakes, of less than 50 hectares in size each, that are distributed throughout its urban fabric.

Berlin’s ecosystems face challenges related to the city’s rapid densification and climate change. In particular, many of those small lakes suffer from the increased ocurrence of temperature and rain extremes.

Urban lakes are crucial sources of freshwater for humans and can have tremendous ecological benefits. On one hand, they are home to a variety of aquatic and terrestrial plants and animals, making them important biodiversity hotspots. They are also climatic refuges, helping to help cool down cities by reducing the heat island effect, and provide spaces for leisure, which support citizens physical and mental health.

Berlin is considered a “green city”. 30% of its total area is covered by forests and other green spaces. 6% is covered by water. The latter comprises not only the Spree-Havel river and lake system, but also more than 300 small lakes, of less than 50 hectares in size each, that are distributed throughout its urban fabric.

Berlin’s ecosystems face challenges related to the city’s rapid densification and climate change. In particular, many of those small lakes suffer from the increased occurrence of temperature and rain extremes.

Urban lakes are crucial sources of freshwater for humans and can have tremendous ecological benefits. On one hand, they are home to a variety of aquatic and terrestrial plants and animals, making them important biodiversity hotspots. They are also climatic refuges, helping to cool down cities by reducing the heat island effect, and provide spaces for leisure, which support citizens physical and mental health.

Urban lakes, however, face a greater threat: lack of monitoring.

Lakes smaller than 50 ha are not part of the monitoring and action cycles of the EU Water Framework Directive, and accordingly only receive higher attention in individual cases.

No simple methods were known to identify particularly polluted lakes, to investigate the type of pollution and to prioritise and evaluate measures.

“Solutions driven by combining available data and deploying AI technologies offer great potential to improve the management of small urban lakes, identify drivers and indicators for stressors of water quality and make better informed decisions”

Malte Zamzow

Researcher, KWB

People monitoring the condition of a lake using an mobile phone app.

The AD4GD Approach

Combining IoT, citizen science and Earth observations for improved decision making

AD4GD has developed a Water Quality Index (WQI) for polluted small urban lakes by combining IoT, citizen science and Earth observation data with AI technologies to identify drivers and indicators of water quality stressors. A Water Availability Index (WAI) has also been created by combining Earth observation data with IoT measurements and citizen science-based assessments of water levels. All data is validated ensuring compliance with the FAIR principles. All these insights are displayed in a user-centered Graphical User Interface called Splashboard, enabling stakeholders to better assess Berlin’s small lakes, identify those with the greatest management needs and prioritizing actions for current and future challenges based on more informed decisions.

Determining trophic status with remote sensing data

There are many Copernicus products based on Sentinel-2 data that determine water properties, including turbidity, chlorophyll content, and water level. AD4GD developed a new index to estimate the trophic status of lakes called the “normalized difference trophic index“. It is calculated by combining three years of data about the trophic status of the lakes, obtained from the Sentinel-2 L2A product. Trophic growth is determined over an entire growing season. This method was developed using 294 lakes greater than 50 hectares in Brandenburg, Germany (see Deliverable 4.2 and Zamzow et al., 2025). Applying this method to 42 Berlin lakes, AD4GD was able to rank their condition from 2018 to 2024 and identify trends (see Deliverable 6.2). This can be used, for instance, to evaluate the effects of remediation measures.

Citizen Science as lake monitoring support

Two different methods of data collection were developed for interested citizens to participate even without much experience or prior knowledge. On the one hand, qualitative data can be collected via the CrowdWater app, freely available for registered users. A questionnaire was created in close consultation with Berlin stakeholders, including inquiries about the lake biotope, water quality and water availability. The answers are translated into indicators for assessing water quality in terms of nutrients, biotope, use, and risk of water scarcity.

On the other hand, simple measurements of nutrients and conductivity were carried out by citizens at the lake shore using low-budget tests and sensors. The concentrations of phosphate, nitrite and ammonium were measured. Volunteers registered as water rangers at KWB and carried out tests at one lake every one to two months. This supports the work of lake managers, who are unable to monitor all lakes regularly. Find all details in Deliverable 6.2.

Estimating water quality with in-situ oxygen sensors

The oxygen concentration in water is directly linked to the trophic status. Algae and aquatic plants typically produce a peak in oxygen concentration during the day and lower concentrations at night. The difference between minimum and maximum oxygen concentrations at the water surface is expected to be particularly large in lakes with high nutrients levels and high trophic status. AD4GD installed oxygen sensors at a depth of 20 cm during the summer seasons of 2024 and 2025, and oxygen time series of 6 lakes were recorded. The conclusions showed that these measurements can provide interesting insights when viewed over the long term, but they are not suitable for drawing conclusions about the trophic status of small urban lakes through short-term use. Learn more in Deliverable 6.2.

Locating lakes with potential water shortages

The CrowdWater app can be used to locate lakes with water shortages and plan interventions. If rainwater is not directed to sewage treatment plants, it can be used locally as a water source for small lakes. To check this option, a generic stormwater inflow potential was developed that calculates the effective runoff volume of the surrounding areas. Levels of pollution should be considered as rainwater runoff from urban areas is usually contaminated with pollutants and nutrients, which can cause problems in lakes. Read about it in Deliverable 6.2.

Leading partner:

Useful links:

Explore it on GitHub

Access data in GeoNetwork

References:

> Elicegui Maestro, I., Di Pietro, F., Parkhanovich, D., Brobia, A., Maso, J., Hodson, T., & Borger, C. (2025). AD4GD D4.2 Connecting the Green Deal Data Space (initial). Zenodo.

> Bastin, L., Kriukov, V., Lush, V., Serral, I., Hodson, T., Borger, C., & Zamzow, M. (2025). AD4GD D6.2. Pilot Technical Implementation Planning, Implementation and Assessment Report. Zenodo.

> Zamzow, M., Matzinger, A., Rustler, M., and Bastin, L.: Satellite-derived trophic index to support management of small and medium-sized lakes , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20482.

Simplified data flow schema for the water pilot. Author: Diego de la Vega (CREAF).

Splashboard, a user-centered interface

All the data and indices are displayed in a graphical user interface called Splashboard, co-developed with stakeholders using a Human-Centered Design approach.

The interface displays a map of Berlin along with a searchable catalogue of lakes and their trophic state. Each lake has a dedicated page presenting five key widgets: one for metadata, two for trophic indicators, a time series chart for observing historical lake measurements and water level forecasts, and a comment section for user contributions.

Splashboard is currently only available in German. To access the platform, please create an account by providing your name, email and password. Then, log in using your credentials.

Dive into the app