For the fourth straight year, Mallows Bay-Potomac River National Marine Sanctuary joined cities from around the world in the annual City Nature Challenge, which took place from April 24 to 27, 2026.
The City Nature Challenge is a cooperative, friendly competition that brings together communities worldwide to document the natural world using the iNaturalist app. Participants snap photos of plants, animals, and fungi they encounter, uploading them to iNaturalist where the images are logged and crowd-sourced data helps determine the species in each photo.
Each year, the four-day event produces a global picture of biodiversity, with millions of nature observations covering tens of thousands of different species recorded over a single weekend.
