Navigable sections of the Danube:

	Upper Danube  Kehlheim–Gönyű	Middle Danube  Gönyű–Turnu-Severin	Lower Danube Turnu-Severin–Sulina
Length	624 km	860 km	931 km
River-km	2,414.72–1,791.33	1,791.33–931.00	931.00–0.00
Ø slope per km	~ 37 cm	~ 8 cm	~ 4 cm
Height of fall	~ 232 m	~ 68 m	~ 39 m
Vessel speed     upstream	9–13 km/h	9–13 km/h	11–15 km/h
Vessel speed     downstream	16–18 km/h	18–20 km/h	18–20 km/h

 Source: Danube Commission, via donau

Depending on the geological and climatic conditions as well as on the tributaries of the Danube, there are typical differences in the annual average discharge in the three sections of the Danube. Generally, on the Upper Danube the highest water levels are recorded between May and August, and the lowest water levels between October and March. On the Middle and Lower Danube low water levels are observed between August and October and high water levels in the months of April and May.

Discharge near Vienna (reference period: 1961–1990):

	Danube	Danube Canal	Total
Low navigable water level	910 m³/s	70 m³/s	980 m³/s
Average water level	1.915 m³/s	160 m³/s	2.075 m³/s
Highest navigable water level	5.010 m³/s	230 m³/s	5.240 m³/s
Centennial flood	—	—	10.400 m³/s

 Source: via donau (KWD 1996)

Characteristic water levels of the Danube:

LNWL = low navigable water level = the water level reached or exceeded at a Danube water gauge on an average of 94% of days in a year (i.e. on 343 days) over a long-time reference period.

AWL = average water level = the water level which corresponds to the arithmetic mean of the average annual discharge volume for a long-time observation period (e.g. 30 years).

HNWL = highest navigable water level = the water level reached or exceeded at a Danube water gauge on an average of 1% of days in a year (i.e. on 3.65 days) over a long-time reference period.

Apart from the Kelheim–Sulina main route several navigable distributaries, side arms, canals and tributaries form an integral part of the Danube waterway system. In contrast to the section Kelheim–Sulina all other transport routes are national waterways, which are subject to various different regulations.

The following is an overview of these waterways:

Danube distributaries:

• Kilia arm (northern distributary, border between Romania and Ukraine)
• St. George arm (southern distributary, Romanian territory)

Major Danube side arms:

• Bala and Borcea (Romania, left river bank)
• Măcin (Romania, right river bank)
• Szentendre (Hungary, right river bank)

Canals:

• Main-Danube Canal (connection to the river Main and subsequently to the Rhine on German territory)
• Serbian canal network (Dunav-Tisa-Dunav hydrosystem on Serbian territory)
• Danube-Black Sea Canal (connection to the Romanian Black Sea port of Constanţa on Romanian territory)

Major Danube tributaries:

• Váh (Slovakia)
• Drava/Dráva (Croatia/Hungary)
• Tisa/Tisza (Serbia/Hungary)
• Sava (Serbia/Croatia/Bosnia and Herzegovina)
• Prut (Moldova/Romania)