The factors that drive partial migration in organisms are not fully understood. Roach (Rutilus rutilus), a freshwater fish, engage inpartial migration where parts of populations switch between summer habitats in lakes and winter habitats in connected streams.To test if the partial migration trait is phenotypically plastic or has genetic components, we translocated roach from 2 populationswith different opportunities for migration to a lake with migration opportunity, containing a local roach population. Thisenabled monitoring of partial migration of fish in 3 different situations: 1) previous opportunity for migration, migrating ina familiar environment (the local population); 2) previous opportunity for migration, migrating in an unfamiliar environment;and 3) no previous opportunity for seasonal migration, migrating in an unfamiliar environment. In addition, we evaluated themigration patterns of roach in the lake with migration opportunity wherefrom group 2 fish were translocated. Directionalmigration in and out of the lakes was monitored using Passive Integrated Transponder technology. Translocated fish withprevious migration opportunity showed migration patterns more similar to local fish than to their home lake population, andindividuals translocated from the lake without migration opportunity migrated when given the opportunity, suggesting thatpartial migration is phenotypically plastic and triggered by lake-specific environmental cues. We found temperature to bea proximate cue for migration decisions. Individuals without previous migration opportunity migrated at a lower proportionand with different small-scale migration patterns, suggesting that also genetic components are involved in the expression of thepartial migration trait.