The first large-scale public data release from the Herschel-ATLAS survey will occur this year. In this poster we summarise the data that will be available, and we highlight one of the unexpected results from this wide-field sub-millimetre survey. Herschel’s sensitivity to star-forming galaxies over a broad redshift range can be a great advantage for studying galaxy evolution over cosmic time, but the ubiquitous blending and confusion is a significant barrier to identifying counterparts in the optical. By studying the positional offsets between Herschel-ATLAS sources and optical counterparts in SDSS, we find evidence that counterpart identification is further hampered by weak lensing, which induces correlations between Herschel sources and foreground structures traced by SDSS. This has implications for the redshift distribution and luminosity functions of sub-millimetre sources.