Vortices are an interesting feature of fluid motion. William Irvine of the University of Chicago and colleagues have now shown that the helicity of vortices, which is a measure of the degree to which vortex lines wind around each other, can remain constant even in viscous fluids. Helicity is conserved in the absence of viscosity, but can be dissipated in real (viscous) fluids. Observing the twisting, linking and writhing of hydrofoils in water, the team shows that twisting dissipates vortex tubes while writhing and linking conserve them. The result could allow helicity to be manipulated in real fluid flows, with implications for atmospheric flows ranging from turbulence to the formation of tornados.