Drone footage shows rocky islands and debris dotting the surface of Poland's longest river, as experts said water levels had reached a historic low.

Levels in the Vistula River dropped to 25cm, beating a record set during a drought in 2015 – and the short-term forecast suggests the water level will drop further this week.

The Vistula is Poland's longest river, rising in the mountains close to the Czech border and flowing for more than 1,000km to the Baltic Sea.