Europe's second-longest river is running dry.

Record heat and months without rain have pushed parts of the Danube to historic lows. The drought has stranded cruise ships, slowed cargo traffic and hurt tourism across central Europe.

The Danube runs for nearly 2,900 kilometers from Germany's Black Forest to the Black Sea. It passes through 10 countries and serves as one of Europe's busiest waterways.

Samuel Komoly, captain of a ship that sails through Budapest, has spent his life on the river. Komoly said this summer has brought conditions he has never seen.

"In this year there was very little rain. Not only in Hungary, but in Austria, Germany, the Czech Republic... all the places where the Danube collects the water. We had several times low water. But these extreme lows. This is the first time," Komoly said.

Near Gellért Hill, Komoly points to the Hunger Rock. The landmark appears only when the river reaches rare lows. For generations, people have linked it to drought and poor harvests.

"When the rock comes out from the water, then hunger comes, because then there's very little water in the Danube and also very little water on the field. If you go back in time for hundreds of years when the rock came out, then the hunger came," Komoly said.

The effects stretch beyond Budapest.

In Esztergom, about 70 kilometers north of the capital, international cruise ships remain tied to the docks because the river is too shallow. Many passengers complete parts of their trips by bus instead of boat.

River cruises bring about 600,000 visitors to Hungary each year. Those visitors support hotels, restaurants and shops in Budapest and towns along the Danube. Fewer cruises could cost the tourism sector millions of dollars.

Farther upstream in Moča, Slovakia, wide stretches of the riverbed now sit exposed.

Eszter, a tourist visiting from Vienna, said the empty river is difficult to see.

"It is sad there would be cruise ships coming up and down this area. And now you don't see anything, sometimes only the motorboats that's it. It's really sad. To see how our planet is warming and what it's doing to rivers like this one," Eszter said.

Low water has also disrupted cargo traffic.

Near Lupa Island in Hungary, János has operated a ferry and floating restaurant for 26 years. He said navigation has become risky because hidden reefs now sit close to the surface.

"You need to be very cautious. The river is full of reefs. If you don't know exactly where to go, you will run aground and destroy your boat. That's why you only see smaller boats here. I can still navigate because I know this river very well," János said.

Back in Budapest, Komoly watches the depth meter aboard the Thetis.

Near Parliament, it shows just 0.7 meters where the river is normally more than seven meters deep.

Until water levels recover, many larger vessels will remain unable to continue their journeys.