The Foppe di Trezzo WWF Oasis is located on a Site of Community Importance in the town of Trezzo sull'Adda in the province of Milan.

In this area, which covers about 5.5 hectares in the Adda Nord Park on wetlands created by the excavation of clay, a spontaneous recovery occurred of an environment that is commonly found in the mid-Pianura Padana (Po Valley).

An incredible floristic biodiversity can be found in the wetlands, forests and shrubs of the Oasis. The wetlands, covered throughout the year or episodically by water, host vegetation typically found in the ponds (sedges, rushes, cattails, iris, duckweed), in addition to rather rare plants such as the marsh seedbox, (Ludwigia palustris), the floating fern (Salvinia natans) and the carnivorous plant with yellow flowers (Utricularia australis).  

The tree vegetation is dominated in the north and south by black locusts. The central area, largely closed to the public, presents numerous examples of white willow, black poplar, aspen and cherry with a rich undergrowth of shrubs. Even the herbaceous vegetation is extremely rich and diverse.

The Oasis' vast variety of flora supports a rich population of invertebrates. The specimens most commonly seen during visits to the oasis include diurnal butterflies (17 species have already been recorded), the Odonata and Hymenoptera.