A giant peak in the temperature dependence of the screening current is observed in the ac magnetic response of an ultra-pure YBa$_2$Cu$_3$O$_{6.993}$ crystal in a magnetic field. This phenomenon is crucial for understanding the behavior of superconductors under various conditions. The study of this peak effect can provide valuable insights into the underlying mechanisms of superconductivity and its applications in real-world scenarios. Furthermore, the observation of this peak effect in ultra-pure YBa$_2$Cu$_3$O$_{6.993}$ crystal highlights the importance of material purity in the study of superconductivity. The findings of this research can have significant implications for the development of new superconducting materials and devices.