ABSTRACT: Climate change is impacting ice-affiliated marine mammal habitats throughout the Arctic, with sea ice declines reducing traditional haul-out and breeding habitats, putting a premium on alternative useable areas. In the Arctic, ice forms early in the season and is retained late into the spring in coastal lagoons, but little information is available regarding how this nature type is used by marine mammals. This study documents use of a lagoon by 20 ringed seals tracked for an average of 188 d via satellite-linked GPS tags. Overall, tagged seals spent 8.9 ± 0.4% (±SD) of their time per day inside the lagoon, with strong summer and autumn peaks that dropped off in winter and ceased in spring. Inside the lagoon, seals spent significantly larger proportions of their time hauled out and less time diving in comparison to when they were outside the lagoon. Additionally, the seals dove deeper (19 vs. 7 m) and for longer periods (4 vs. 2.5 min) when outside the lagoon, indicating that most feeding took place out in the fjord. However, residency periods in the lagoon of up to 43 d as well as more intense diving than would be expected for transport to and from haul-out areas within the lagoon suggest that ringed seals also feed in the lagoon. Regular opportunistic sightings of ringed seals in lagoons around Svalbard, Norway, together with the quantitative behavioural documentation of lagoon use in the present study, suggest that lagoons may serve as refugia areas, which might become increasingly important as climate change continues to alter Arctic marine ecosystems.