Water management (SDG 6)

The urban farm of Lak'a Uta is an initiative launched by the NGO Fundación Alternativas, which established the first community garden in Bolivia, located in the city of La Paz at an altitude of 3,600 meters above sea level (1-3). The initial plan was to develop the garden on private land, but since the goal was to create an open space accessible to all citizens, the project eventually sought a public location (3). The subdistrict of Cotahuma granted them permission to use the Lak'a Uta park, an abandoned area rendered unusable by two landslides in the previous year (3). Through voluntary efforts and an investment of 2,800 euros, the land was transformed over three years to accommodate 40 plots of 16m² each, with individual families cultivating a variety of vegetables (3).
Now celebrating its 10-year anniversary, the project adheres to many principles of organic agriculture in an urban setting (5). The area has become a biodiversity hotspot, featuring an artificial pond, 16 wild plant species, and 39 fauna species, including 34 bird species, two types of frogs that provide natural pest control, and three bee species (3-5). Compost is produced naturally using waste management practices and worms (4-5). In addition to edible vegetables, the garden produces medicinal plants, some of which help stabilize the soil and prevent further landslides (3-4). The infrastructure also includes a rainwater collection system (3-5).
Originally, the project aimed to improve access to food, particularly in response to the growing urban population (1-3). Over time, it has also fostered a strong sense of community, while promoting urban gardening through educational workshops and disseminating information nationwide (1-5). It is estimated that 20,000 people have been educated on urban agriculture, healthy eating, and reconnecting with nature (5). The project has also contributed to shaping a local government law supporting urban gardening within the municipality (3).

Thessaloniki, Greece's second-largest urban center, is a key hub for economic growth and outward trade in the Balkans. The city hosts the country’s second-largest export port, which plays a crucial role in connecting European trade routes with Asia and China. However, until 2014, Thessaloniki's waterfront was poorly maintained, largely inaccessible, and unattractive. Moreover, major flooding events, connected to extreme weather events, exposed significant deficiencies in the city's flood mitigation infrastructure, leading to damage to housing and critical services. (5, 10, 11)
To address these issues, the Municipality of Thessaloniki launched an International Architectural Competition for the redevelopment of the New Waterfront. From 2006 to 2014, Thessaloniki's waterfront underwent a significant regeneration aimed at benefiting the city's population of 1.1 million and stimulating the local economy. The revitalized waterfront now stretches 3 kilometers between land and sea, featuring 58,000 acres of green space an playgrounds.. In total, 2,353 new trees and 118,432 plants were added across an area of 238,800 m² (Refs 1, 3, 4).
The project also introduced walking routes, sports and recreational facilities, seating areas, and scenic viewing points. The waterfront now has a bicycle path along the entire walkway, and an arbour of 660 umbrella pine trees, serving as shade from the midday sun. Completed in 2014, the New Waterfront has already become a vibrant urban green space, enjoyed by both Thessaloniki's citizens and visitors alike (Ref 4).

Biotope City Wienerberg is located in the southern part of Vienna on a 5.4-hectare site that once housed a Coca-Cola factory. It lies at the edge of the Wienerberg recreational area, surrounded by business parks and tower blocks to the west and predominantly detached houses to the east (Ref. 1).
The project embodies the concept of an "urban biotope" (Ref. 2), grounded in the principle that nature's mechanisms of self-regeneration are essential for mitigating the challenges of urban living and climate change. By integrating urban and natural spaces, Biotope City fosters both human-nature connections and social interactions through activities like community gardening. The project’s centerpiece is its extensive green infrastructure, including trees and green roofs, which serve to cool the microclimate, purify the air, enhance water retention, and create carbon sinks while providing habitats for local wildlife. These green spaces aim to improve physical health through cooling effects on hot days and support mental well-being with their calming influence (Ref. 1; Ref. 2).
Biotope City encompasses:
Around 980 flats, including 400 subsidized flats and 200 SMART flats
A school, a kindergarten, and 2,000 square meters of children's and youth playgrounds
600 square meters of community gardens and 3,850 square meters of ground-floor gardens
250 trees, 8,900 square meters of meadows, and 13,600 square meters of green roofs
2,200 square meters of façade greening
The inner courtyards and roof areas are designed for gardening, while façades are greened, and balconies are equipped with integrated plant troughs. Even the spaces between buildings are climate-effective, featuring unsealed catchment and seepage areas to manage water sustainably (Ref. 1).
The project’s implementation took 18 years and involved collaboration among various stakeholders. The concept was initiated by the Biotope City Foundation and funded by eight different investors (Ref. 2).

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).

Masthuggsparken is a planned park in the Masthuggskajen district, which is undergoing development and construction. The park will measure about 2000 m2, and serve as a green oasis and meeting place for locals. It will have ameneties such as benches and areas for play, and a noise barrier against a large nearby road. The park will connect to the adjacent square and street, making it accessible to visit. The street will be renovated to have more trees and plants, increasing green connectivity in the district. The park will be surrounded by trees and other plants, which are planted to promote biodiversity and be adapted to a changing climate [Ref. 1-5, 7]. The park is at a low point, where up to 800 m3 of stormwater will flow during heavy rainfall, reducing flood risk in the surroundings [Ref. 1, 2, 6]. The Masthuggskajen district has a sustainability program, establishing goals for green environments which the park will contribute to. Green areas should be accessible to the entire district and provide ecosystem services such as rainwater management, climate adaptation, biodiversity and recreation. The program was created by the City of Gothenburg in collaboration with construction companies active in the area and was supported by Citylab Action, a national competence program in sustainable urban development [Ref. 7]. The City of Gothenburg is the primary responsible for the park, which will be constructed between 2025 and 2026 [Ref. 1, 2, 4].

The "Tree Plantation Month" is an annual national initiative in Romania, organized by the Ministry of Environment, Water, and Forests through the National Directorate of Forests. This initiative focuses on afforestation, forest regeneration, and raising awareness about the ecological benefits of forests, while promoting sustainable behaviors (4, 9, 10). Having been in place for 60 years, the program has recently aligned with the principles outlined in the 1991 Paris Declaration on the Sustainable Development of Forests (10). At the national level, the initiative is regulated with overarching goals aimed at protecting and sustainably managing Romania's forests (9). The program allows for the involvement of various actors, including public institutions, municipalities, NGOs, and schools, who collaborate with regional forestry directorates to implement local activities (4).
In 2019, as part of this initiative in Iași, the Asociația Tineretul Ortodox Român Iași (ATOR), a youth-led religious association, actively participated in one of the campaigns . They planted 1,000 tree saplings in the Moara de Vânt district, an area that had suffered from deforestation and was prone to landslides (1, 2). The afforestation efforts were designed to address these environmental challenges by stabilizing the soil, reducing the risk of overflow and flooding, maintaining soil moisture, and regulating extreme temperatures (1). To ensure long-term success, the saplings were regularly monitored, and restoration efforts were carried out in cases where the trees were affected by fires or drought (3).

The "EnRútate por el Ambiente" initiative is a collaborative strategy implemented in Cartagena through a partnership between Ecopetrol, EPA Cartagena, and the Cartagena Refinery. The initiative aims to promote sustainable community development in neighborhoods adjacent to the refinery by addressing key environmental challenges such as pollution and the degradation of water bodies and green spaces. Its overarching objective is to improve quality of life through the promotion of sustainable practices and environmental stewardship (ref 5).
The strategy is structured around three programs. The first component focuses on the management of public spaces for recreation and environmental care. The second, Guardians of the Channels, seeks to empower local residents as promoters of water body conservation within their communities. The third program promotes the engagement of all community members, including schools and educational institutions, through participatory environmental initiatives (ref 1).

The South Hennepin Marsh habitat restoration project, located below the Grosse Ile Toll Bridge causeway, within the Detroit River's Trenton Channel near Grosse Ile, Michigan, aims to restore and protect one of the region's most critical wetland habitats. This emergent marsh, historically vital for fish and wildlife, has suffered significant degradation due to river currents, boat traffic, and winter ice flows. The project, identified as a priority in the 2002 Habitat Protection and Remediation report for the Detroit River, encompasses the restoration of over 1,000 linear feet of protective shoals and 20 acres of productive wetlands, home to various native plant species such as rushes and submergent macrophytes.

The primary goal of the project is to stabilize and enhance the marsh's habitat, improving conditions for fish, waterfowl, reptiles, amphibians, and other wildlife. Restoration activities include the placement of approximately 10,000 cubic yards of rock and soil to rebuild eroded shoals, installation of erosion matting, and re-establishment of native vegetation. Additional habitat features, including habitat logs, mudpuppy structures, and stone spawning beds, will provide crucial breeding and feeding areas for species such as walleye, northern pike, and lake whitefish.

The project also incorporates soft engineering solutions, such as fallen branched trees and strategically placed stones, to support pollinators, birds, and reptiles. Feasibility studies and design plans were completed by Environmental Consulting and Technology, with funding from NOAA, and construction was carried out by E.C. Korneffel Company beginning in 2021. The project reached completion in November 2022, successfully restoring the shoals and protecting the marsh from further degradation. These efforts have significantly enhanced habitat availability, ensuring the sustainability of the South Hennepin Marsh as a critical ecological site within the Detroit River system.
(Ref.1-4)

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 project to revitalize the Huveaune River and its biodiversity is taking place in Aubagne, a city within the Marseille Metropolitan area. For a long time, the river received little attention, constrained by urbanization, and was even covered for several hundred meters. Urbanization and the construction of a road have made the floodplain more susceptible to flooding (Ref 2). The initiative aims not only to restore the Huveaune and its environment but also to strengthen the connection between residents and the river (Ref 1) while reducing flood risk as a critical objective (Ref 1).
The challenge is transforming the area into a higher-quality environmental space with resilient ecosystems. A diagnostic conducted during the project's design phase revealed the site's degraded state, including the presence of invasive species, steep banks unsuitable for riparian vegetation, poor waterway conservation, and disrupted ecological continuity (Ref 2).
Key actions include revitalizing the river and its biodiversity, removing artificial banks, and creating new meanders to give the river a more natural shape. Diversifying flow patterns will create habitats for aquatic and fish species by varying water heights and flow speeds. This involves increasing the river's sinuosity and varying the width of the minor riverbed (Ref 2). Additional steps include planting trees and shrubs adapted to the Mediterranean climate with low water needs (Ref 2). To bring residents closer to the river, plans include creating walking and cycling routes, sports equipment, educational panels, and useful visitor facilities such as benches, water points, and restrooms (Ref 3).