The Thayamühlbach is a canal constructed in 1300 that branches off from the Thaya river at Krhovice/Gurwitz and after a scant 32 km reenters the Thaya at Hevlín/Höflein. In its course it not only enters Austrian territory but actually runs right through the city centre of Laa an der Thaya.
The Thayamühlbach twice makes use of an aqueduct in its course, and the national border serves as the main contour of the canal in several places. Along its length it serves several mills and small power stations with hydropower. It also serves several fisheries, such as the Upper and Lower Jaroslavice pond (Horní and Dolní Jaroslavický rybník). About 20 km upstream is the most important mill, the Slup Mill. It was constructed in the Middle Ages by the local Müller Brotherhood in the renaissance style that still determines its current appearance.
During the Communist period the agricultural cooperative ground corn there until 1957. After the Fall of the Wall it was declared a national cultural monument in 1993. In order to best use the water power of the canal in the face of technical developments, it has been rebuilt numerous times over the centuries, for the last time in the 1830s.
Today it is a noteworthy technical monument.