The Wadąg is a river which rises from a lake of the same name near Olsztyn. Flowing out from the southern edge of the reservoir it goes west and reaches the city. Here, it flows through the City Forest and at the same time marks the northern administrative borderline of the city. After about 9 km it joins the Łyna as its right-sided tributary.

Before it flows into Wadąg Lake, the river is called Pisa Warmińska and flows through Barczewo. It is supplied by two picturesque rivers – the Dadaj and the Kośna – the extension of which is called Kanał Kiermas (the Kiermas Channel). All of these currents have popular kayak trails. The river Wadąg is their connection with the Łyna, on which the trails may be continued.

Along the first part of the Wadąg stretch numerous allotments. Later on, the river flows under a bridge which has had its appearance on television. It is the same bridge as the one from which a speeding car falls into the water in the opening credits of the TV series "Stawka większa niż życie" (Stakes Larger than Life). Two hydroelectric power stations from the XXth century should also be taken into consideration. They dam up the water and, as a result, increase the dynamics of the river's current.