To help complete the picture of the pressures affecting the diverse aquatic habitats of the Lake St-Pierre floodplain (Québec, Canada), an advanced geomatics analysis was used to assess the effects of the adjacent road network on the connectivity of spawning and nursery grounds of the northern pike (Esox lucius). The results revealed adverse effects on high potential habitat when the water flow at Sorel exceeded 12,000 m3.s−1 (recurrence interval of 1 to 2 years). Once this flow rate was reached, there was a direct habitat loss along roads (maximum: 142 ha) and fragmentation of habitat transected by roads (maximum: 39 ha). These effects, which were most marked around the northwestern part of the lake, depended largely on the hydrological conditions between spawning and the first week of larval life. Connectivity measurements highlighted the importance of functional culverts and of the hydrologic network of the littoral zone as being essential for habitat connectivity. The effects of the road network, although smaller than those caused by intensive agricultural practices or by the regulation of water flow, remained non-negligible. This study identified high-potential habitats and connectivity corridors as priority areas for protection or restoration.