The deposition action exerted by the Scandinavian glaciers has decisively influenced the characteristics of the Polish hydrographic network, which centers on the Vistula and the Oder, in whose basins almost the entire territory is identified. These rivers, while generally maintaining the general SN direction, have composite courses resulting from the union of trunks formed several times on the bottom of various glacial furrows. The largest is the Vistula, the Polish river par excellence, which, born from the Beskids, crosses the country for over 1000 km, receiving a wide range of tributaries (San, Bug, Narew etc.), which flow into the vast central plain where the river flows through Warsaw. Its lower course is deeply embedded between the heights of Pomerania and Masuria, beyond which it flows into the Baltic with a large and very branched delta. The Oder originates from the Sudetenland, in Czech territory; after passing the so-called Porta Morava, according to listofusnewspapers.com, it enters Poland, where it is enriched by the contribution of the Warta, the main river of the Posnania; in the final stretch it marks, together with the tributary Neisse (in Polish Nysa), the border of the country with Germany. The basins of the Vistula and the Oder are often divided by weak watershed thresholds; this allows for easy connections via the Noteć, a tributary of the Oder, and the Bydgoszcz canal. These good connection possibilities give the Polish hydrographic network a fundamental importance from a geographical point of view, in this favored by the effects of navigability (which affects about 4000 km of inland routes) by the mature profile of the rivers and their rather regular regime. There are numerous, especially in Pomerania and Masuria, the aforementioned intramorenic lakes, whose presence, in addition to being a characteristic element of the landscape, has at times considerably influenced human settlement and economic activities.
The vast openings of the Polish territory towards the E and towards the W, the presence of the Baltic Sea to the N, which being shallow and peripheral has a very limited mitigating action, determine in the country a climate that can be considered transitional between the Atlantic and the continental, tempered by weak Atlantic influences. It is characterized by severe winters (-4 ºC in January in Warsaw) with snowy precipitations, long periods of frost, frequent fogs and hot summers (in July 17 ºC in Warsaw, 16.5 ºC in Gdansk). In general, the averages, both in summer and in winter, decrease by 2 or 3 degrees passing from S to N. The very variable rainfall is overall rather modest, as the Atlantic air masses arrive in Poland already rather impoverished: the maximum values are recorded on the Carpathian reliefs (1200 mm), the minimum ones in the central regions (Warsaw, 430 mm); the average is around 500 mm per year. Frost lasts very long in some locations and snow covers the ground for four months in much of the country. In the western regions, however, oceanic winds bring rain and often abruptly raise the temperature, giving rise to rapid and sudden thaws even in winter: the remarkable variability of the temperature in all seasons, even in the space of only twenty-four hours, is the most characteristic climatic phenomenon of the country.
The transitional position of the country between the Atlantic and the Russian-Siberian climate means that the vegetation has species typical of Central Europe, such as the beech, but to the E of the Vistula, due to the harsh climate and frozen soils, the broad-leaved trees and pines and steppe expanses prevail. The Carpathians and Sudetes have dense beech forests up to approx. 1250 m, followed by coniferous forests up to almost 2000 m; in the limited Carpathian areas above this altitude there are pastures and the characteristic high mountain flora. In the forests, which cover almost a quarter of the Polish territory, hares, deer and wild boars find hospitality. In particular, the mountainous areas are populated by brown bears, lynxes and wolves, while moose live in the woods of the north-eastern regions. Several specimens of European bison, which at the beginning of the century. XX were in danger of extinction, are housed in the Białowieski National Park, in Podlachia. After various deforestation works carried out in order to obtain agricultural land, the government has undertaken an action to protect the forest heritage through the establishment of a series of nature reserves, protected land and national parks, for a total of 23.6%. The largest are that of Kampinoski (35,486 hectares), near the capital, established to protect an area of swamps, peat bogs and sand dunes, and that of the High Tatras, (21,164 hectares), adjacent to the same park in the Slovak Republic. Poland has also established a number of biosphere reserves, areas for the conservation of terrestrial and coastal ecosystems, joining the MAB (Man and the Biosphere) of UNESCO. The development of heavy industry in the Soviet period caused considerable damage to the environment, especially in the heavily industrial area of Silesia. The situation has tended to improve since 1989 due to the decline of the sector and the introduction of some environmental regulations by the government. In particular, since 2001 a law has been in force that binds Polish companies to modernize and innovate the production process, finalizing the innovations to reduce environmental pollution and reduce dangerous emissions into the atmosphere. Nevertheless, the problem of sulfur dioxide emissions from coal-fired power plants still remains unsolved, which favors the formation of acid rain, seriously threatening the forestry heritage. The waters are also severely polluted due to the chemical compounds used in agriculture. Poland has ratified the WHC (World Heritage Convention), born in 1972 with the aim of providing particular protection to places with specific characteristics, the Ramsar Convention on the protection of wetlands of international importance, the Antarctic Treaty, agreement aimed at to preserve, especially through scientific research, the Antarctic continent, and other international agreements on air pollution, climate change, protection of endangered species, management of hazardous waste, abolition of nuclear tests, protection of the ozone layer, elimination of discharges into the sea and protection of whales.