Location
"Dolina Ploni and Jezioro Miedwie" refuge is the Site of Community Importance which covers the area of 21253.9 ha. The site is located south-east of Szczecin. The Plonia river valley stretches from sources near Barlinek to a village of Kolbacz together with valleys of two tributaries of the Plonia: the Strzelica and the Krzekna rivers. Southern part of the valley lies within borders of Barlinecko-Gorzowski Park Krajobrazowy (the Barlinek-Gorzow Landscape Park). One of the biggest lakes in Poland - Jezioro Miedwie (35 km²), which also serves as a drinking water intake for Szczecin - is situated in the river valley.

Landscape
The site is divided into two units of different origin, geomorphological composition and structure of habitats:

• "Zrodliskowa dolina Ploni" has  a gorge character. It is a deep valley which cuts across marginal frontal moraine. High and steep slopes are cut through by numerous ravines and little erosive valleys. Communities of deciduous forests, mostly Central European oak-hornbeam forests, mixed forests and Luzulo-fagetum beech forests dominate on slopes and in ravines. Upper edges are occupied by semi-natural dry grasslands and scrubland facies on calcareous substrates and warm oak forests lobes.
• "Basen Pra-Miedwia" encompasses area of the Plonia and the Krzekna valley within so-called pleistocene ice-marginal lake and basal moraine. The surrounding terrains are characterized by not too big height differences and very fertile soils.

Upper part of the Plonia valley consists of valuable spring areas. Many wet calcareous meadows occur in the valley, usually characterized by extremely rich flora. After the end of agricultural use rapid succession of hydrophilous tall herb fringe communities, sedge communities and willow scrubs took place within parts of the valley. Regulation of watercourses in the valley contributed to creation of wide meadow areas. Only few streams were preserved in their natural condition. Meadows, intensively used in the past, are currently overgrowing. Moreover, peatlands are being destroyed and the quality of drinking water is being worsened by the creation of fishponds.

Ecosystem
Dolina Ploni and Jezioro Miedwie is a site of large biodiversity. Occurrence of 17 kinds of habitats from 1 Appendix and 11 species from Appendix 2 of the Habitats Directive has been confirmed here. Among the most important biotopes of the refuge are carbonate swamps, developed in waters and at shores of lakes, locally enriched by halophilic species.

Habitats present within Dolina Ploni site:

• hard oligo-mesotrophic waters with benthic vegetation of Chara spp.
• alkaline fens
• alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae)
• natural eutrophic lakes with Magnopotamion or Hydrocharition-type vegetation
• lowland hay meadows (Alopecurus pratensis, Sanguisorba officinalis)
• molinia meadows on calcareous, peaty or clavey-silt-laden soils (Molinion caeruleae)
• calcareous fens with Cladium mariscus and species of the Caricion davallianae
• hydrophilous tall herb fringe communities of plains and the montane to alpine levels
• sub-continental steppe oak forests
• Luzulo-Fagetum beech forests
• riparian mixed forests of Quercus robur, Ulmus laevis and Ulmus minor, Fraxinus excelsior or Fraxinus angustifolia along the great rivers (Ulmenion minoris)
• semi-natural dry grasslands and scrubland facies on calcareous substrates (Festuco Brometalia) (important orchid sites)
• xeric sand calcareous grasslands (Koelerion glaucae)
• water courses of plain to montane levels with the Ranunculion fluitantis and Callitricho-Batrachion vegetation
• rivers with muddy banks with Chenopodion rubri p.p. and Bidention p.p. vegetation
• petrifying springs with tufa formation (Cratoneurion)

Flora
Significant part of the site is covered by shallow and stagnant inland waters, meadow and scrub habitats and forests. Qualities of the area include well preserved streaked layout of biotopes with a full range of typical plant communities with characteristic species, such as: floating water plantain, fen orchid, summer adonis, sand leek, snowdrop windflower, European columbine, lord and ladies, European wild ginger, common water-starwort, bellflower, Bohemian sedge, Buxbaum's sedge, weak Arctic sedge, seaside centaury, early marsh-orchid, western marsh-orchid, fringed pink, crested fern, marsh helleborine, star gentian, autumn gentian, dune gentian, sharp-flowered rush, blunt-flowered rush, marsh pea, martagon lily, Asian flax, twayblade, bird's nest orchid, military orchid, hairy milk-vetch, lesser butterfly orchid, Jacob's ladder, primula eliator, wind flower, brookweed, brown bog-rush, black bog-rush, purple viper's grass, feather grass, globe flower and cow soapwort.

Fauna
Many species of birds live within the area including: aquatic warbler, kingfisher, lesser spotted eagle, bittern, black tern, white stork, marsh harrier, hen harrier, Montagu's harrier, whooper swan, ortolan buntig, great snipe, crane, white-tailed eagle, little bittern, red-backed shrike, smew, black kite, red kite, ruff, golden plover, barred warbler, wood sandpiper.

Amphibians and reptiles are also widely represented in Dolina Ploni. We can come across: fire-bellied toad, great crested newt, slow worm, common toad, sand lizard, viviparous lizard, grass snake, tree frog, Alipne newt, common viper, pool frog, moor frog, laughing frog, common frog, edible frog.

Moreover one can also meet here: Eurasian beaver, otter, lesser white-toothed shrew, European water shrew, as well as representatives of two species of bats - the Nathusius' pipstrelle and Daubenton's bat.

Threats and protection
Greatest part of the area is not under protection. However, two nature reserves exist within the site: Brodogory and Stary Przylep, as well as a part of Barlinecko-Gorzowski Landscape Park with "Skalisty Jar Libberta" nature reserve and a fragment of "Barlinek" Area of Protected Landscape.

There are projects to establish 15 nature reserves: Zrodla Ploni, Gradowa Dolina, Wilcze Jary, Janowskie Murawy, Wawozy pod Zydowem, Legi Zrodlikoskowe pod Chrapowem, Woldowo, Lubiatowskie Legi, Kluki, Laki Strorczykowe nad Jeziorem Szybel, Laki Ramienicowe Jeziora Koryto, Modre Klociowisko, Turze, Miedwanski Brzeg and Koszewo.

Major threats to the site include: fluctuation in intensity of meadow use, expansion of acreage of arable land, abandonment of traditional, extensive way of using meadows, drainages, fall of groundwater level, building fishponds, peat exploitation, deforestation or spontaneous overgrowing of grasslands.