Loctaion
The refuge is located on Mazowiecka Lowland, in Vistula valley, only several kilometers to the southern east from Warsaw.

History and Landscape
Bagno Calowanie was created on avalanche terrace of Vistula River valley and is heavily supplied with underground waters. It stretches on the stripe with width of 3 km and length of 15 km. The thickness of peat reaches 4 m. This area has been used by a human for a long time. Sedge areas were mowed every year for hay and litter, and pastured so that forest could not grow here. The peat was also extracted here in a small range, small water reservoirs occurred in the appeared pits. However the most of the area was dried up to now, but the natural vegetation remains in good conditions.

Dunes are very characteristic element on this plain area, which often grow even few meters above the meadows. They cut the fens with the strip running from north to south. The biggest dune is called Pekatka.

Ecosystem
Open meadows' gatherings dominate in the landscape, they occupy more than a half of the refuge's area. Most of them is constantly agricultural use, but they start to overgrow by forest. Molinia meadows with such rare species like: Siberian iris (Iris sibirica), fringed pink (Dianthus superbus), early marsh-orchid (Dactylorhiza incarnata) and marsh gentian (Gentiana pneumonanthe) occure here. There is Betula humilis growing on the fens, it is endangered with extinction and included in Red List of Threatened Plants. You can meet thermoohilic grasslands with wind flower (Pulsatilla pratensis), purple-stem cat's-tail (Phleum phleoides) and spiked speedwell (Veronica spicata) on dunes. Vast areas are overgrown by willow thickets, and also by alluvial and boggy forests (mainly on the north part).

Torfowisko Calowanie is the important refuge for birds. Eurasian curlew, black-tailed godwit, corn crake, marsh and Montagu's harrier, honey buzzard, common crane, black stork, lesser spotted eagle nest here. You can meet beavers and elks on the peatbogs.

There are 11 types of habitats from Appendix I of Habitat Directive which occupy 60% of the area. Among species occurring here 6 are listed in Appendix II of Habitat Directive.

Threats
- drainage of the ground,
- desisting of traditional methods of extensive agriculture: mowing and pasturing,
- peat and sand exploitation,
- creating wild waste dumps in peat holes,
- building fish ponds,
- plans of fen's commercial arrangement (race-track, entertainment centre, highway etc.)

Nature Protection
The refuge is situated on the area of Mazowiecki Landscape Park. Small part of fens is under protection in "Na Torfach" reserve, which was established in 1977 and encompasses surface of 21 ha.