Abstract: Based on the geostrophic current fields calculated from altimetry data for the period from January 1, 2013, to December 31, 2023, numerical modeling of advection of potentially contaminated water from the Kashiwazaki–Kariwa Nuclear Power Plant to the shores of Primorsky Krai and the fishing zone around the Southern Kuril Islands was carried out using a Lagrangian approach. Dasymetric maps demonstrating likely pathways of the surface contamination of the ocean were constructed. Transport pathways and three corridors related to the local current structures and mesoscale eddies were identified for the southern Primorye region. The minimum advection time for Lagrangian markers, simulating potentially contaminated waters, to reach the coast of Primorsky Krai was estimated at 138–140 days. Two possible transport routes into the Southern Kuril fishing zone were revealed, with the potential for rapid advection of contaminated markers into this zone within 58–60 days. The advection of Lagrangian markers occurs in portions and within specific time windows.