Achieved improved water quality

The "Ventanilla Wetlands" Regional Conservation Area (ACR) is an area of 275.45 hectares protected and administered by the Regional Management of Natural Resources and Environmental Management of the Regional Government of Callao (1, 2). It was established on December 20, 2006, by Supreme Decree No. 074-2006-AG, to conserve a representative sample of the coastal wetlands of the Subtropical Pacific Desert (2). With an ecosystem shaped by various hydrological and ecological processes, the "Ventanilla Wetlands" ACR is home to 126 bird species and 27 native plant species, making it an ideal area for ecotourism, recreational, educational, scientific, and cultural activities, thanks to its landscapes and biodiversity (2). However, the Ventanilla Wetlands face several challenges due to urban growth, water pollution, waste, traffic and plane overflights from the National Police and Navy, leading to a decline in bird populations due to noise exposure (5).
This area is fed by the hydrological system of the Chillón River, by surface waters from the Sedapal oxidation ponds, and by water seepage from nearby human settlements and populations adjacent to the wetland. The Ventanilla Wetlands are also influenced by the marine system, especially in the northwest zone. This gives the ACR area lagoon-like characteristics, meaning that its waters are slightly brackish despite being separated from the sea. The internal hydrological system supports the growth of species such as cattails, bulrushes, and reeds. In total, there are 27 native plant species, which serve the function of filtering and purifying the wetland's water. Additionally, the flora provides protection and food for various fauna species, particularly birds, with 126 species recorded, including resident and migratory birds from the Andes, local areas, and the Northern and Southern Hemispheres. Moreover, this protected natural area is home to five reptile species, including endemic species from Lima that are endangered (3).

The Fairy Garden, also known as the WOW Recreational Park, is a distinctive green space located near Diósgyőr Castle in Miskolc, Hungary. Since its opening in April 2020, the park has quickly gained popularity, earning third place in the 2020 Tourism Attraction of the Year award in the professional category. Once a neglected and polluted site with historical significance, the area was transformed by a local entrepreneur. After removing over sixty containers of waste, including hazardous materials, a park was created that harmonizes with the natural environment, preserving existing willow trees and integrating water features fed by local streams. When creating the park, the creators respected the plants of the area to the maximum, not a single tree was cut down, and the fruit trees were also kept.
The park boasts various decorative elements, including a carousel, a garden cinema, and other amenities. However, in September 2021, it was closed indefinitely for renovations. Gábor Vaszil, the lessee who had rented the land from the Miskolc municipality, intended to purchase the property for further development. Despite initial support from the local government, the transaction was halted due to concerns raised by the regional Water Management and Protection Authority regarding the protection of Miskolc's drinking water resources. Their ongoing investigation has delayed any further decisions about the sale or the future of the park. In the meantime, the garden remains open to the public for leisurely walks, similar to other municipal parks in Miskolc.
(Ref.1-4)

On the site of a former malthouse in Berlin, a company has developed a sustainable rainwater storage system to prevent flooding in the sealed environment, which had been vacant for several years. Once used for malt production, the site is now home to offices, studios, manufacturing businesses, and hosts sustainable events. The site's transformation includes natural gardens, tenant gardening beds, green roofs, and two outdoor water basins that retain rainwater, creating a blue space for recreation. (Ref. 1)
The two ponds are filled with filtered rainwater, and an underground tank stores additional water, allowing it to seep away gradually. Native plants surround the ponds, creating a habitat for local wildlife. Given that much of the surrounding area is sealed, the ponds help mitigate urban flooding by managing and storing rainwater, reducing the site's reliance on the urban sewage system. Additionally, as Berlin faces extreme heat in summer, the project offers a cooling effect and provides access to filtered water during droughts. (Ref. 1; Ref. 2)
The project is managed and financed by IGG Malzfabrik mbH, which oversees the entire site in Berlin's industrial area and rents out office spaces to various companies. This initiative is part of a broader sustainability strategy that addresses social, economic, and ecological factors, and it is featured in the company’s common good economy report (Gemeinwohl-Ökonomie Bericht). (Ref. 5)

Torslanda School is a newly built elementary school (years 0-6) where the schoolyard includes innovative ways to manage rainwater. The school was initially part of the Rain Gothenburg project, which aims to make the city, and this school, the best in the world when it rains. It was also a pilot project within the city's "equal building" initiative, aiming to make indoor and outdoor environments accessible and attractive to everyone regardless of gender identity, functional diversity or age [Ref. 1]. The main element of the schoolyard is a "river" to which water will be led when it rains, combining stormwater management with opportunities for play and education. The system will retain about 310 m3 of water and treat it before releasing it to a recipient. The river will be used to teach the children about climate, ecology, biodiversity and the water cycle. The river and schoolyard are connected to a natural wetland [Ref. 3, 4]. The school is run by the City of Gothenburg, who initiated the project, employing an architecture firm and a construction company to design and build the school and schoolyard [Ref. 3-5].

The "Mangle Verde" project is a community-led intervention aimed at reforesting mangrove areas in Cartagena, particularly around the Ciénaga de la Virgen and Ciénaga de Juan Polo. Initiated by Gloria Sánchez and other members of the Villa Gloria community, this project is a response to the environmental degradation caused by urban development, including the construction of a viaduct, and the damages inflicted by invasive settlements and pollution​(ref 1,4). The primary goal of the project is to restore the mangrove ecosystems, which are essential for maintaining water quality, preventing coastal erosion and supporting marine biodiversity conservation (ref 4). In addition, this initiative provides socio-economic benefits by fostering ecotourism and increasing fish populations, which directly benefit the local fishing economy​(ref 1). The "Mangle Verde" project emerged as a grassroots response to compensations granted by the Concesión Costera for the damage caused by infrastructure projects in the region. Local residents of Villa Gloria, recognizing the importance of the mangrove ecosystem, established nurseries in their homes where they cultivate three types of mangroves (ref 2,4). So far, the initiative has planted over 26,860 mangrove saplings and is committed to continuing the reforestation efforts, which also include cleaning and maintaining the canals around the mangroves​ (ref 1). Beyond ecological restoration, the project also addresses key environmental risks in Cartagena, including coastal flooding and habitat degradation, driven by both natural phenomena (e.g., tides) and human activities such as urban sprawl and illegal dumping (ref 6, 7).

In an architecturally important area of Berlin, situated between the Landwehr Canal, the Kulturforum (the Berliner Philharmonie and the Berlin State Library) and the new construction on Potsdamer Platz, a combination of green and grey infrastructure has been realised to minimise the burden on Berlin’s existing water infrastructure.
Green and non-green roofs harvest annual rain, which flows through the site’s buildings and is used for toilet flushing, irrigation, and fire systems. The roofs retain and then release water to the large on-site buffer pond, which has five underground storage tanks. Next to the roofs, a series of urban ponds and connecting canals have been implemented, with a combined area of approximately 1.2 hectares. They are filled with rainwater, creating an oasis for urban life. Vegetated biotopes are integrated into the overland landscape and serve to filter and circulate the water that runs along streets and walkways. The lake’s water quality is excellent, forming a natural habitat for animals and cooling the surroundings, while fresh water usage in the buildings has been reduced. (Ref. 1; Ref. 2; Ref. 3; Ref. 6)
The project was implemented in the 1990s as part of the development of Potsdamer Platz in the wake of the reunification of Germany. Several architects collaborated on the implementation that was completely privately funded. Beyond its ecological and technical features, the site is a blue natural site in the heavily built city centre of Berlin and allows people to linger and enjoy natural features. The drainage system won several sustainability prices and is considered a successful integration of nature and technology-based mechanisms to foster climate change adaptation. As the rainwater system stores rainwater in underground tanks and ponds, the urban sewage system is relieved during heavy rain, and water can evaporate. Therefore, the small water circle is closed, and the microclimate is cooled. (Ref. 2; Ref. 6)

The 28th of October Street (28ης Οκτωβρίου) was one of the most neglected streets on the eastern side of Thessaloniki, completely devoid of trees despite its central importance. Additionally, the street suffered from severe flooding during heavy rainfall. In 2011, the Municipality of Thessaloniki, in collaboration with Konstantinos Zervas, the Deputy Mayor for the Environment, Quality of Life, and Free Space, proposed a redevelopment project aimed at transforming the street through the planting of trees and the installation of flower beds that would function as rain gardens (Refs 3, 5). This initiative was part of the "Integrated Green Cities" action, which falls under the European territorial cooperation program Greece-Bulgaria 2007-2013 (Refs 1, 2, 3, 6).

To achieve the dual goals of sustainable rainwater management and urban beautification, decorative trees were planted in specially constructed bioretention tree stands. These stands, along with the flower beds, were designed to collect rainwater, which would then be used to irrigate the trees along the road and the plants forming the rain gardens. Rainwater was gathered from the road surface, pavements, and the gutters of apartment buildings through these bioretention systems (Refs 1, 2). This sustainable water management solution significantly reduced rainwater runoff, improved water quality, and enhanced the area’s aesthetic appeal (Refs 2, 6, 7).

Miskolctapolca is a district of Miskolc and features a nature park (which includes a lake, Csonakazo-to) originally planted in the 1920s using the exotic trees and bushes. In 2022 the municipality decided to renovate the area under a EU funded project called "Creating a Green City in Miskolc-Tapolca". The project aimed to establish a modern urban green space focused on active recreation for various age groups, enhancing Miskolc's appeal for tourism.
The renovation included new concrete paving system and updated utilities for the lakes' promenades with a strong emphasis on accessibility ensured smooth mobility throughout the area. The renovation added informative signs detailing local attractions, historical trees, and the park's history. To enhance visitor comfort, a new accessible restroom was constructed. Renovations to the Csonakazo-to lake included removing accumulated silt and reinforcing the shoreline, alongside the addition of new street furniture, lighting, and wooden sunbathing terraces and platforms. The two bridges around the lake were renewed, and the squirrel installation, a favorite among locals, were restored. Furthermore, a square in the park, Kilátó Square was transformed with benches and drinking fountains, creating a welcoming space for relaxation.
Additionally, extensive landscaping was carried out, including the planting of approximately 100 trees, 9,000 shrubs, 18,000 perennial plants, 2,300 annuals, 350 roses, and 6,600 bulbs.
The surrounding park, which had been in disrepair for decades, was thoroughly revitalized, blending traditional and modern aesthetics. This long-overdue renovation significantly enhanced the environment. The construction was carried out by FEDRID Építőipari Kft., starting in spring 2022, and was completed in May 2023 after some delays.
(Ref.1,2,3)

The Olaya Herrera neighbourhood in Cartagena has been the focus of a series of projects that involve ecological restoration, environmental education, and community resilience building. These initiatives have centred around the restoration of the Ciénaga de la Virgen, an ecologically significant but heavily degraded coastal wetland bordering the neighbourhood. The primary goals of the projects in Olaya Herrera include the restoration of degraded mangrove ecosystems, mitigation of flooding and water pollution, strengthening community participation in environmental management, and promoting sustainable urban environments (ref 1, 2). The project is led by the EPA Cartagena, which coordinates actions such as collecting solid waste, planting timber trees and ornamental plants, and restoring green spaces that had become informal dumping grounds (ref 1). It also includes a community-led initiative called Los Guardabosques de Olaya that focuses on reforestation and environmental stewardship, it involves children, youth, and local mothers in reforesting mangrove areas around the Ciénaga de la Virgen. The community has established a mangrove nursery and employs innovative waste management practices, such as installing traps in canals to prevent solid waste from entering the Ciénaga (ref 2). The project also involves the private sector in 2022, the EPA led a campaign with local companies like Konfirma, Acuacar, and Pacaribe that focused on improving environmental health through the removal of 10 cubic meters of waste, promoting healthy living environments and fostering community participation in environmental monitoring and waste management practices​ (ref 4). Also, in collaboration with community leaders and local companies, the ANDI-TRASO Alliance supports large-scale reforestation and restoration activities in the southern parts of the Ciénaga de la Virgen adjacent to Olaya Herrera. The alliance plans to plant 40,000 mangrove seedlings (ref 6).

Situated in the southern suburbs of Kunming City, Dianchi is one of the largest freshwater lakes in Yunnan and the sixth largest in China (Refs 1, 2). However, due to rapid industrial development, agricultural activities around the lake, land reclamation, and population growth, Dianchi Lake became severely polluted, ranking among the most contaminated lakes in China. This pollution threatened biodiversity and degraded natural habitats (Refs 1, 2, 3). The introduction of exotic species further disrupted the lake’s ecological balance (Ref 1).
In response, the Kunming Institute of Zoology (KIZ), with funding from the Chinese Government, World Bank and the Global Environment Facility (GEF) launched the Lake Dianchi Freshwater Biodiversity Restoration Project. This initiative aimed to restore natural habitats, improve water quality through biological means, and foster community engagement and institutional capacity, creating a sustainable framework for the long-term conservation of Dianchi's unique freshwater biodiversity (Refs 1, 4).
The project was implemented across four key components: Wetland Management and Restoration, Surveys and Monitoring of Species Conservation, Capacity Building and Training, and Public Awareness (ibid.). The project was rated 'Satisfactory' in terms of outcomes, sustainability, and execution under a comprehensive evaluation framework that employed multiple indicators (Refs 4, 5).