We have developed an alternative cold-adapted (4, 8 °C), Arctic/Alpine inoculum to overcome the obstacle of limited hydrolysis and methanogenesis that is common in low temperature anaerobic wastewater (WW) treatment systems. This special WW-fuelled inoculum was employed here to study its activity and growth at low temperatures (4 and 15 °C) with real wastewater as substrate. Cell specific methanogenic activities (4–15 °C) were comparable with those observed for mesophiles at higher temperatures (37 °C) (≈2.0 gCODmethane.gVSS−1.day−1). Low temperature (4 °C) acclimation forms methanogenic communities that perform robustly at 4 °C and better than those pre-acclimated to higher temperatures (8 °C) when incubated at 15 °C. An evaluation of the inoculum resistance to migration of ‘outsiders’ at low (4–8 °C) and high (15 °C) temperatures showed that the lower the temperature the higher the probability for migration (archaeal migration rate at 4–8 °C 1.69 × 10−5 death−1 > 6.44 × 10−6 death−1 at 15 °C). Limited cell growth at low temperature treatment systems is one of the main reasons. This limitation can be overcome as growth kinetics at low temperatures (4 °C) are comparable to those observed in mesophilic reactors (≈20 days – growth coef.: 0.05 day−1) depending on the substrate availability. Thus, continuous, rich in COD feeding regimes may assist cold adapted biomasses to not only grow at low temperatures but also to decrease the probability to be outpaced by of WW-originated ‘invaders’.