City Nature Challenge at Mallows Bay

May 26, 2026

For the fourth year in a row, Mallows Bay-Potomac River National Marine Sanctuary participated in the worldwide City Nature Challenge that occurred from April 24 to 27, 2026. The City Nature Challenge is a friendly collaboration among cities all over the world to share observations of nature using the iNaturalist app. Participants upload photos of the plants, animals, and fungi that they see, where it gets recorded in iNaturalist while crowd-sourced data helps identify the species. Each year, the City Nature Challenge provides a snapshot of global biodiversity, with millions of observations of tens of thousands of different species across the world recorded over one weekend.

a person takes a photo of a turtle using their cell phone
Photos uploaded to iNaturalist help record biodiversity in the sanctuary. Photo: Taylor Schneider/NOAA

As part of the City Nature Challenge, sanctuary staff and partners held a BioBlitz at Mallows Bay Park on April 26, where participants joined to collect species observations in the sanctuary. A BioBlitz is an event that focuses on finding and identifying as many species as possible in a specific area over a short period of time. All observations collected at the sanctuary during the BioBlitz are counted towards the Washington, D.C. region totals for the City Nature Challenge. During the event, sanctuary partners offered a variety of engaging activities for participants, including guided hikes led by Walk Charles County and Southern Maryland Audubon Society, and an electrofishing survey to record fish species by the Smithsonian Environmental Research Center Fisheries Conservation Lab.

two women stand in front of a sign that says Bioblitz with the national marine sanctuaries logo
Research and Outreach Coordinator Megan McCabe and Mallows Bay Park Manager Elena Gilroy pose with the BioBlitz sign. Photo: Elena Gilory/Charles County

Nearly 40 people participated in the BioBlitz, collecting 237 observations of 167 different species of plants, birds, reptiles, fish, amphibians, and more. Since the first BioBlitz at Mallows Bay in 2023, these annual events have added over 1,500 observations of hundreds of different species in the sanctuary and Mallows Bay Park to iNaturalist. These records help sanctuary staff and co-managers better understand the species diversity and ecology of the sanctuary, and provide insight into the presence of invasive and endangered species.

The annual BioBlitz coincides with Citizen Science Month in April, National Volunteer Week, and National Environmental Education Week. Community science events like the BioBlitz provide an opportunity for volunteers to visit the sanctuary, learn more about its ecology, and contribute valuable scientific data to research and monitoring programs.

Interested in lending a hand? Learn more about community science programs at Mallow Bay-Potomac River National Marine Sanctuary, and check out more opportunities to get involved in your national marine sanctuaries across the U.S. this spring.

Megan McCabe is the research and outreach coordinator for Mallows Bay-Potomac River and Monitor national marine sanctuaries