The is a river in Poland and the Czech Republic, a right tributary of the River Oder. It flows from the Silesian Beskids mountains through southern Cieszyn Silesia in Poland and the Frýdek-Místek and Karviná districts of the Czech Republic, often forming the border with Poland. It flows into the Oder River north of Bohumín. The Olza-Oder confluence also forms …The is a river in Poland and the Czech Republic, a right tributary of the River Oder. It flows from the Silesian Beskids mountains through southern Cieszyn Silesia in Poland and the Frýdek-Místek and Karviná districts of the Czech Republic, often forming the border with Poland. It flows into the Oder River north of Bohumín. The Olza-Oder confluence also forms a part of the border.