Exploiting a large French panel for 1976-2007, we examine the impact of low-educated immigration on the labour market outcomes of blue-collar natives initially in jobs where immigrants became overrepresented in the last decades. Immigrant inflows generate substantial reallocations of natives across locations and occupations. Location movers are negatively selected while occupation movers are positively selected and move towards better paid-jobs characterised by less routine tasks. As a result, controlling for composition effects has an important quantitative impact on the estimated effects of immigration. Low-educated immigration generally lowers the wages of blue-collar workers, but its impact is heterogeneous across sectors.