Fusion scientists at DIFFER, together with an international team of groundwater researchers, have written a paper on new ways to determine how fast groundwater enters or exits the river. This is directly related to how the temperature in the riverbed changes. By measuring the temperature at different soil depths, they can determine the relevant heat transport parameters. And that is something that is also done frequently in fusion research. An interview with Ricky van Kampen and Matthijs van Berkel.