Аннотация:Wave attractor, a phenomenon of internal/inertial wave self-focusing in a stratified/rotating fluid in non-trivial geometry, leads to the rapid turbulence development due to the energy accumulation on a limited area. It was believed until now that instability in a wave attractor should develop in the Triadic Resonance Instability way. In this work it is shown that in a specific geometry, close to real water basins geometries, the instability behaviour can sufficiently differ from that observed in a trapezoid setup.