The Gaißa is a river in Bavaria

Bavaria

Bavaria, formally the Free State of Bavaria is a state of Germany, located in the southeast of Germany. With an area of , it is the largest state by area, forming almost 20% of the total land area of Germany...

, southeastern Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

, tributary of the Danube

Danube

The Danube is a river in the Central Europe and the Europe's second longest river after the Volga. It is classified as an international waterway....

. It flows through the Bavarian Forest

Bavarian Forest

thumb|The village of Zell in the Bavarian ForestThe Bavarian Forest is a wooded low-mountain region in Bavaria, Germany. It extends along the Czech border and is continued on the Czech side by the Šumava . Geographically the Bavarian Forest and Bohemian Forest are sections of the same mountain range...

 from North to South, crosses Aicha vorm Wald

Aicha vorm Wald

Aicha vorm Wald is a municipality in the district of Passau in Bavaria in Germany....

 and joins the Danube northwest of Passau

Passau

Passau is a town in Lower Bavaria, Germany. It is also known as the Dreiflüssestadt or "City of Three Rivers," because the Danube is joined at Passau by the Inn from the south and the Ilz from the north....

. Thereby the river reaches a length of approximately 25 kilometres. Due to the nearby motorway much dirt was flushed into the water from time to time. Meanwhile its grade is B quality.