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A laboratory experiment was conducted to investigate the characteristics of turbulence generated by an internal wave ray breaking on a sloping bed. The width of the incident wave ray was small compared to the bed length, so that an isolated turbulent patch was generated by the breaking process, a configuration unique to the present study. The parameter range covered subcritical, critical and supercritical frequencies. Flow visualization and velocity measurements revealed that near critical conditions the flow was confined to a narrow region above the bed and, contrary to expectations, critical waves showed a weak turbulence field. Subcritical and supercritical reflection resembled wave–wave interaction between the incident and the reflected waves and showed comparable centred displacement lengthscales. As the incident waves became progressively supercritical instabilities were first initiated away from the …