The presence of COVID-19 face masks in the largest hypersaline lagoon of South America is predicted by urbanization level.

The inadequate disposal of face masks has caused a widespread presence of COVID-19 litter in the environment. We monitored 10 beach arcs along approximately 15 km of the largest hypersaline lagoon of South America looking for face masks during the lockdown (2021) and in the "new normal" (2022) period. Our working hypothesis is that the probability of finding face masks increases with higher urbanization levels, which was estimated by the Human Modification Metric. Approximately 3 × 10 face masks m were found on nine of 10 beaches (90 %) during the lockdown. However, this reduced to 1 × 10 face masks m found in eight beaches (80 %) after the lockdown. The probability of finding a face mask was significantly higher as urbanization increased (z = 2.799; p = 0.005). This situation imposes the need for a better waste management and environmental education actions, targeting the reduction of direct littering on coastal ecosystem.