The Warta Mouth National Park (Polish: Park Narodowy Ujście Warty) is the youngest of Poland's 23 national parks. It was created on 19 June 2001 in the region of the lowest stretch of the Warta river, up to its confluence with the Odra (Oder), which marks the Polish–German border. The park covers an area of 80.38 square kilometres (31.03 sq mi) within Lubusz Voivodeship.

The park was created on the area of the former Słońsk Nature Reserve, which had existed since 1977, and parts of the Ujście Warty Landscape Park. The ground here is swampy and muddy, which makes it a haven for birds. This is why the former Słońsk preserve, which is now part of the park, was in 1984 covered by the Ramsar Convention, whose purpose is to protect such areas.

The park has its headquarters in the village of Chyrzyno, near Kostrzyn nad Odrą.