This is difficult to determine, nor is it measured by the level of the river by catching and then measuring the water level from the bottom of the riverbed, but by measuring the depth of the river from the lowest water level ever measured. That is, the so-called water gauge never touches the bottom of the riverbed. Somewhere I read that if the water level in Budapest is, say, 8 meters, it can be as high as 14-16 meters in some sections of the river. Of course, the depth of the Danube cannot be determined exactly, as it can vary from week to week by several meters.