The River Vistula is Poland’s longest, and also the longest river flowing into the Baltic Sea. It is 1,047 km long. The Vistula flows into the Gulf of Gdańsk, its average annual mouth area flow according to Tczew metering station data reaching 1,046 m³/s. Vistula headwaters are located in southern Poland, on the west slope of Mount Barania in the Silesian Beskid mountain range. Geographically speaking, the Vistula is fed by two source creeks: the Biała (White) Wisełka (1,080 m ASL) and Czarna (Black) Wisełka (1,107 m ASL). In hydrological terms, the Vistula runs from where the Malinka brook joins the Wisełka creek formed by Biała and Czarna Wisełkas, both flowing into Lake Czerniańskie. Unnavigable, the upper section of the Vistula – below the River Przemsza estuary – is referred to as Little Vistula.

The river is divided into three courses: (1) upper course, from the source to Zawichost (below River San confluence), (2) middle course – Zawichost to River Narew confluence (in operational terms, frequently defined as running to the Włocławek barrage), and (3) lower course – from the Narew confluence (or Włocławek barrage) to the estuary.

Vistula’s final lower course comprises the river’s delta. In the village of Biała Góra near Sztum, around 50 km from the mouth, bifurcating into distributaries: Leniwka (to the left) and Nogat (to the right), the Vistula forms a broad delta called Żuławy (Fenlands). Prior to the 14^th century, Vistula’s estuary was divided into Wisła Elbląska (Elbląg Vistula, main east distributary) and Wisła Gdańska (Gdańsk Vistula, smaller west distributary). Wisła Gdańska has been officially recognised as the main distributary since 1371. In early modern times, Vistula’s main and secondary distributaries had been referred to as Samica and Lacha, respectively. In the wake of the flood of 1840, a new distributary developed: Wisła Śmiała (Bold). A cross-ditch was excavated near Świbno and the river’s mouth over the years 1891-1895.

The River Vistula’s basin is 194,424 km² in area.

The River Vistula valley crosses multiple forest complexes as well as protected areas and zones, including the Nature 2000 area. Protected areas located directly in Vistula’s proximity include the following:

• Special-purpose bird protection areas,

• Special-purpose habitat protection areas,

• Nature reserves,

• Landscape parks,

• Protected landscape areas.

The Vistula River valley comprises the Kampinos National Park buffer zone as well.

Flanking the boundaries of Bydgoszcz and directly exposed to the adverse impact of the “Zielona” waste landfill complex of the former “ZACHEM” S.A. Chemical Plant, the Vistula River Valley in the Lower Course Nature 2000 area is recognised as north Poland’s natural heritage, comprising ornithological territories of European importance, as well as fish, amphibian and mammal habitats. No less than forty-four species listed by Annex I to the Birds Directive and four Polish Red Book species can be found locally. The Valley is a breeding area for approximately 180 avian species, and a pivotal habitat for migratory and wintering birds. During the mating and breeding season, the Valley is inhabited by at least 1% of Polish white-tailed eagle, common merganser, common shelduck, little tern, common tern, common kingfisher, and Eurasian oystercatcher populations.

Rich in nature, this picturesque area, including the River Vistula’s watershed course across the Southern Baltic Lake District, is directly threatened with natural environment degradation. The humongous risk of degradation to the Vistula River Valley in the Lower Course Nature 2000 area is associated with contaminated groundwater migration from Bydgoszcz in the general direction of the River Vistula, and on to the Baltic Sea. Groundwater diagnosed as contaminated is directly linked to the many years of production at the former “ZACHEM” S.A. Chemical Plant in Bydgoszcz. Particularly typical factors involved on-site development of multiple contamination clusters, extraordinarily diverse in terms of substances recognised as a threat to the soil-and-aquatic environment, and/or migrating within its perimeter. Frequently associated with high toxicity potential, the production of chemicals, organic and inorganic alike, generated multiple options for contamination to permeate into the soil-and-aquatic environment. Groundwater and soil studies carried out across the former “ZACHEM” S.A. Chemical Plant site have identified a considerable rate of pollution, mainly caused by toxic substances.

In the wake of the Plant’s bankruptcy, operational infrastructure has been undergoing continual destruction, contamination outreach expanding daily. Generated by the migration of toxic, mutagenic and cancerous substances, health and environmental threats remain the region’s largest issue. Substances coming in direct contact with the local community (residents of the Łęgnowo-Wieś and “Awaryjne” residential housing estates and local villages of Plątnowo and Otorowo) include i.a. phenol, aniline, toluidine, chloroaniline and diphenyl sulphone, as well as inorganic substances, such as chlorides, sodium and sulphates. The issue is exacerbated by hydrogeological conditions typical for river valleys, where the groundwater table shallows out on the floodplain, remaining right beneath the surface.

The remediation project has been mainly designed to treat the frontal section of the polluted groundwater plume generated by the “Zielona” waste landfill complex. The chosen remediation technology is unique in that it allows the removal of a broad spectrum of organic contamination rather than a single chemical (such as phenol). Multifaceted technological effects produce improved physical and chemical soil, land and groundwater parameters, not to mention reduced organic contaminant concentration rates. Once reached, the target will warrant reduced health and environmental threats, to the Nature 2000 area in particular.