Why Are the Danube, Sava and Tisa Below Navigable Levels?

Can the Danube, the Sava and the Tisa all drop below navigable levels at the same time? They can, and that is exactly what is happening. The Republic Hydrometeorological Service (RHMZ) issued a hydrological warning this morning, August 24, saying water levels on all three rivers will stay below low navigable levels in the coming days. Alongside them sits a long list of smaller waterways that have already hit what hydrologists call the biological minimum.

The new warning goes a step further than what we have reported so far. Until now we had only tracked the Danube’s water level at Bezdan, which had fallen to minus 168 centimeters. This is the first time RHMZ has grouped the Danube, the Sava and the Tisa near Titel into a single warning, alongside a longer list of tributaries across inland Serbia.

Which rivers have already hit their biological minimum?

Besides the three major rivers, the institute is also flagging flows that have dropped close to the minimum mean monthly values with 95 percent unreliability, a threshold hydrologists refer to as the biological minimum. The list includes:

• the Kolubara and its tributaries
• the Jadar
• the Toplica
• the Vlasina
• tributaries of the Zapadna Morava
• tributaries of the Velika Morava
• the Crni and Beli Timok

In the hydrological warning issued on August 24, RHMZ states:

Water levels on the Danube, the Sava and the Tisa near Titel will run below low navigable levels in the coming days.

Why are water levels falling so sharply?

The cause has been the same all summer: a prolonged stretch of high temperatures without meaningful rainfall. For the rest of August, the institute is forecasting daily highs of 30 to 35 degrees Celsius, with temperatures above 35 degrees already expected today and tomorrow in the south and southeast of Serbia, before the heat spreads to the rest of the country on Friday and Saturday.

The same drought that is draining the rivers is also keeping fire risk high. RHMZ says in the same warning:

High temperatures, combined with a rainfall deficit and occasional strong wind, will continue to dry out vegetation and keep the risk of open fires starting and spreading elevated.

This isn’t a new story, just a worse one

The Danube has already been breaking records this summer. On the stretch between Bezdan and Slankamen, the river was measured 139 centimeters below its reference level, its lowest point in fifty years. The shallow riverbed has made cargo traffic on the river difficult, and in parts of Europe shipping has been temporarily suspended, since moving goods at such low water levels no longer pays off.

What is new in this morning’s warning is that the problem is no longer confined to the Danube. The Sava and the Tisa have now joined it, and smaller rivers inland are, by hydrological standards, already at the edge of what they can sustain.

What this means for you these days

If you’re planning a river trip or a weekend by the water, expect this summer’s beaches and sandbanks to have shifted, with shallows wider than you remember. For households near the Kolubara, the Jadar, the Toplica or the Timok, this is a good reminder to use water sparingly during this stretch, since the same system that draws water from your tap often draws it from the river downstream as well. And with temperatures still above 30 degrees, the risk of open fires outdoors remains high, so an open flame in nature is the easiest thing to avoid these days.