Low-Redshift Interlopers in the SDSS DR16 z > 5 Quasar Catalogue

High-redshift quasars (z>5) are crucial for studying early black hole growth and reionisation. SDSS Data Release 16 catalogues 655 such sources with multiple redshift estimators. We systematically examined this subsample and found 480 sources (73.2%) where pipeline redshift (Z DR16Q) disagrees with the derived estimate (Z FIT) significantly. Visual inspection confirms that 125 of these (19.1% of the total) are actually low-redshift active galactic nuclei. In 114 cases, broad Mg, ii with C, iii and C, iv was misidentified as Ly α; in 11 cases, H α was misidentified as Ly α. This error is immediately revealed by the absence of Gunn--Peterson trough blueward of Ly α. Crucially, Z FIT recovers correct redshift in the affected sources where emission lines are prominent, indicating the algorithm is sound; the issue lies in community preference for Z DR16Q or Z SPEC. We urge caution against uncritical use of pipeline redshifts for z>5 DR16Q sources and recommend Z FIT as the preferred estimator.