In the government's document ‘Assumptions for the development plans of inland waterways in Poland for 2016-2020 with an outlook until 2030’, a plan was announced for a significant improvement in navigation conditions on the Vistula River waterway - connecting Gdańsk with Warsaw and forming part of the international E-40 waterway. It has been estimated that the costs of this development will amount to PLN 31.5 billion . Furthermore, the ‘European Agreement on the Main Inland Waterways of International Importance’ – signed by the President of Poland in January 2017 – obliges to take steps to achieve at least IV international navigability class on the Vistula.
The first step in the implementation of the Vistula waterway is the construction of a new dam. Therefore, already in December 2017, the interministerial 'Agreement on the implementation of the investment in the construction of the Siarzewo dam' was signed . In the same month, the Regional Directorate for Environmental Protection (RDOŚ) in Bydgoszcz issued a positive decision on the environmental conditions for the implementation of the dam project prepared by the state-owned company Energa. The decision was made immediately enforceable, as the documentation assessed the investment in the category of activities for the benefit of significant social interest. The point is that, according to the construction of the new barrage, the main goal is to ensure the lasting safety of the neighboring Włocławek dam, which has been operating since 1970. The new utility is to dam up the waters to an elevation of 46.0 m above sea level. The building in Włocławek, which is the only implementation of the great communist project 'Cascade of the Lower Vistula', operates in conditions of river bed erosion and exceeding the permissible water levels above the dam, which in extreme situations may result in a catastrophe. In the official discourse, the following were considered side effects of the dam investment in Siarzewo: ensuring the transport function, stopping the progressive deep erosion below the Włocławek dam, increasing flood safety in the Włocławsko-Ciechocińska valley, reducing the risk of ice blockages, preventing the steppe-formation of Kujawy region and using the energy potential of the river (there will be a power station) .
The main investor – the State Water Holding Polish Waters – argues that it will have minimal impact on displacements and on land ownership. Only 20 plots of land have been identified in three communes where the existing buildings collide with the planned location of the investment and its facilities .
The planned location of the investment is the village of Siarzewo (Vistula: rkm 706-707). The reach of the backwater will extend upstream, to the Włocławek dam (Vistula: rkm 674-675). The new dam will affect a large part of the Kuyavian-Pomeranian Voivodeship, i.e. the following counties: Toruń, Aleksandrów, Lipno, Włocławek and Włocławek (a city with county rights). The investment zone will include three Natura 2000 areas: ‘Włocławska Dolina Wisły’ (PLH 040039), ‘Nieszawska Dolina Wisły’ (PLH 040012) and ‘Dolina Dolnej Wisły’ (PLB 040003). Moreover, it is located within the Protected Landscape Area of the Ciechocin Lowlands and the ‘Zielona Kępa’ ecological site .
In the decision of the RDOŚ, it was determined that the introduction of such a large hydrotechnical construction into the environment would have a significant negative impact on nature. Willow, poplar, alder and ash riparian forests will be destroyed as a result of their logging and dehumidification. It was assumed that there will also be stats in oxbow lakes and natural eutrophic water reservoirs. It was also found that the habitats of 7 species of protected birds (the little tern, the common tern, the little ringed plover, the common sandpiper, the European herring gull, the common gull and the kingfisher) are impossible to save. The population of certain species of fish is also threatened: Amur bitterling, spined loach, European river lamprey and Atlantic salmon. Therefore, the RDOŚ decision assured that the implementation of the investment would be accompanied by environmental compensation . Riparian forests on an area of over 500 ha, oxbow lakes (40 ha) and sandy inland islands (70 ha) are to be restored. This document also specifies mitigation measures, including the construction of the bypass bed of the barrage with a river character similar to the natural one, ensuring the possibility of migratory fish migration. The construction of fish passes for ichthyofauna was also planned and the location of construction back-up and access roads in the areas of water intake protection zones was forbidden. As part of the restocking, 250,000 Atlantic salmon smolt and 10,000 individuals of sea trout will be released into the river annually .
Between 11 and 30 January 2018, eight environmental organizations and user of the fishing circuit lodged appeals against the decision of the RDOŚ. The allegations concerned the assessment of the impact of the investment on the possibility of preserving natural habitats and species constituting the objects of protection of Natura 2000 areas. It was argued that the dam would lead to the destruction of all spawning grounds in the reservoir cap, while cutting off from the spawning grounds located in the upper reaches of the Vistula River, thus preventing its reproduction. It was also alleged that the scope of the provided compensation does not meet the natural needs, and in some places its effectiveness is questionable or inadequate to the subject of protection for which the compensation was provided for. They also pointed to errors and inaccuracies in the analysis of variants and alternatives. The appellants also raised objections relating to the procedural sphere of the proceedings. For example, the documentation completely ignores the fact that cemeteries will be located in the area of rising groundwater levels. There was also no assessment of the impact on these cemeteries, and no remedial measures were indicated .
Many environmental defenders believe that the Siarzewo dam does not have to support the Włocławek dam, which in 2013-2015 was modernized for PLN 115 million. They indicate that there is no risk of catastrophe there. They also think that the construction of another partition on the Vistula River may increase the risk of winter jam floods, which will occur in two places at once – on the Włocławek and Siarzewo reservoirs. Moreover, they are covinced that the proposed dam will increase the risk of drought, because below the resulting reservoir, the erosive force of the water will wash out the material from the bottom, lowering its level. This will lead to a decrease in the water level in the river and, consequently, in the groundwater, which will cause droughts locally. The Siarzewo reservoir will also have no impact on the irrigation of the fields. All because of its location: the fields lie on an escarpment, the reservoir – in the valley. Investment opponents also claim that the dam is not a response to the country's energy needs. The investment costs of installing the planned turbines are at least 6 times higher than investments in solar or wind energy    .
The new dam and the associated hydroelectric power plant will also contribute to increasing greenhouse gas emissions - organic matter deposited on the bottom as a result of decomposition in anaerobic conditions will emit, among others, methane. The amount of these gases released per unit of generated energy may be up to 4 times higher in the case of hydropower plants (dam reservoirs) than in the case of conventional coal-fired power generation  .
The project documentation lacks an analysis of the problem that may turn out to be of key importance for the inhabitants of the area in the immediate vicinity of the planned investment, i.e. mass emergence of bloodworms (Chironomidae). Today, they are a nuisance for the inhabitants of the Włocławek Reservoir, making investments and places attractive to tourists (e.g. summer houses and marinas) useless .
Numerous ecological organizations stood up to fight the main investor. In 2018, the collective ‘River Sisters’ was invented as a protest to publicize the demands of the Save the Rivers Coalition (operating since 2017). This women’s group envolved from the collective 'Polish Mothers on the felling', founded a year earlier, against the controversial ‘Szyszko’ Act. The artistic message was clear: to save the Vistula, which is in danger of being blocked by a great dam in Siarzewo, her sisters and other rivers come. The women gave the rivers a voice and emphasized their subjectivity, recalling their names. To become the ‘River Sisters’, you just need to wear blue and hold a sign like a road sign with the name of your river in your hands. In addition, women sew and present bathing suits with a "pro-river" message embroidered on them, thanks to which they gained popularity in the media. The ‘River Sisters' are supported by 'Brothers Torrents'   .
On March 15, 2021, representatives of these two groups – as well as other organizations from the Save the Rivers Coalition – protested at the headquarters of the Ministry of Infrastructure in Warsaw. Several dozen people manifested in response to the announcement of a tender for the construction of the Siarzewo dam . On April 17, 2021, near the river port in Nieszawa, there was a protest of swimmers from all over Poland.
Not all scientists are against dam construction. Moreover, this project is supported by some local government officials, entrepreneurs, various institutions and private persons. During the lobbying campaign conducted, among others, by in the diocese of Włocławek, the activists of the Union of Kujawy Land Communes gathered over 100,000 endorsement signatures .