This experimental study brings the turbulent length scales and the Reynolds stress anisotropy into focus in wall-wake flow downstream of an isolated dunal bedform. The results reveal that wall-wake flow downstream of an isolated dune possesses a high-turbulence level having its peak value at the dune crest level. This level lasts up to the vertical distance until the effects of the dune on the flow disappears. Regarding the turbulent length scales, downstream of the dune, the Prandtl’s mixing length in wall-wake flow is greater than that in undisturbed upstream flow, while the Taylor microscale and the Kolmogorov length scale are smaller. In Reynolds stress anisotropy analysis, the anisotropy invariant maps demonstrate the data plots form a looping trend in wall-wake flow. Below the dune crest, the turbulence is characterized with an affinity to show a two-dimensional isotropy, while above the crest, the anisotropy has a tendency to reduce to a quasi-three-dimensional isotropy. © Springer Nature Switzerland AG 2020.