German children have been flocking to an inlet of the Baltic Sea lured by the promise of frolicking with a dolphin.

Hundreds of children have swum with the dolphin since Friday, some even taking rides on its back.

The dolphin has been moving back and forth between the Kieler Förde and the Kiel canal in Schleswig-Holstein, northern Germany, holding up ships and boats as it swims alongside them to move through locks.

Witnesses have reported that the dolphin is very friendly and allows swimmers to embrace it, and even pulls people through the water. Some said it appeared to beckon children to play by nudging them with its nose.

A dolphin swimming with bathers near Kiel. Photograph: Thomas Eisenkraetzer/EPA

“The dolphin is merrily making its way in and out of the sluice,” said Mathias Visser, of the Waterways and Shipping Office. “It gives the impression that it’s in a good way. It doesn’t seem to bother the shipping traffic.”

But the Waterways and Shipping Office issued a warning for bathers not to swim too close to the locks.

The Institute for Baltic Sea Research said it suspected the dolphin had been swept in during the winter of 2014, when violent storms forced about 200tn litres of North Sea water into the Baltic Sea, the biggest saltwater inflow for 60 years.

Researchers are trying to establish the dolphin’s origins.