Three-color image of the M 17 SW PDR taken by NACO at three near-IR broadband filters (blue: H; green: K; red: L), with the area of the SINFONI integral field spectroscopy outlined in the white box. Individual point sources discussed in this paper are labeled. Three types of maser are marked according to their coordinates: 22-GHz water masers (filled triangles, Caswell 1998; Johnson et al. 1998); Class II methanol masers at 6.66 GHz (filled diamonds, Caswell et al. 1995, 2000); OH masers at 1.67 GHz (thick plus, Caswell 1998).