We present a detailed study of emission-line systems in the GAMA G23 region, making use of $textit{WISE}$ photometry that includes carefully measured resolved sources. After applying several cuts to the initial catalogue of $sim$41,000 galaxies, we extract a sample of 9,809 galaxies. We then compare the spectral diagnostic (BPT) classification of 1154 emission-line galaxies (38$%$ resolved in W1) to their location in the $textit{WISE}$ colour-colour diagram, leading to the creation of a new zone for mid-infrared warm galaxies located 2$sigma$ above the star-forming sequence, below the standard $textit{WISE}$ AGN region. We find that the BPT and $textit{WISE}$ diagrams agree on the classification for 85$%$ and 8$%$ of the galaxies as non-AGN (star forming = SF) and AGN, respectively, and disagree on $sim$7$%$ of the entire classified sample. 39$%$ of the AGN (all types) are broad-line systems for which the [ion{N}{ii}] and [H$alpha$] fluxes can barely be disentangled, giving in most cases spurious [ion{N}{ii}]/[H$alpha$] flux ratios. However, several optical AGN appear to be completely consistent with SF in $textit{WISE}$. We argue that these could be low power AGN, or systems whose hosts dominate the IR emission. Alternatively, given the sometimes high [ion{O}{iii}] luminosity in these galaxies, the emission lines may be generated by shocks coming from super-winds associated with SF rather than the AGN activity. Based on our findings, we have created a new diagnostic: [W1-W2] vs [ion{N}{ii}]/[H$alpha$], which has the virtue of separating SF from AGN and high-excitation sources. It classifies 3$sim$5 times more galaxies than the classic BPT
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