Every day, mammals need to plan and execute efficient actions for survival. We believe the dentate gyrus (DG) of the hippocampus, known to be involved in pattern separation, is critical to distinguish between similar alternative routes to the same goal. We set up a crossword maze in which mice learnt two spatial routes in an alternative manner to reach a unique reward position during a 1-h training session. Chemogenetic inhibition of dorsal hilar neurons using hM4Di induced a poor performance during the learning of one of the routes after mice had found the reward using the alternative path in the previous trial. We then investigated if the dorsal DG was needed for the rapid discrimination between alternative routes to the reward, or whether it also contributed to the learning performance. We thus broadened the expression of hM4Di to the majority of dorsal DG neurons (hilus + granule layer) to get a complete manipulation. Interestingly, inhibition of the dorsal DG only impaired the pursuit of reward in the second learned route, once mice had reached the goal location using the alternative path. All subjects managed to learn the first path in which they have found the reward, regardless of its difficulty. Our results suggest that the dorsal DG may not be important for learning per se of the spatial task. Instead, we propose that the DG may enhance the resolution and identification of similar spatio-temporal information to reach a goal using an optimal strategy.