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City Nature Challenge 2025

Join the international City Nature Challenge (CNC) event and become community scientists in the greater Denver-Boulder Metro region! This annual event motivates people around the world to take observations of the natural world using the iNaturalist app. Last year, more than 83,000 people participated and made 2.5 million biodiversity observations worldwide.

The City Nature Challenge consists of two phases – the Observation Phase – where community scientists use the iNaturalist smartphone app to record observations of nature in their city, and the Identification Phase where nature enthusiasts and experts work to link species identifications to the observations.

Key Dates for the 2025 CNC

April 25-28 | Observation Phase
April 29-May 4 | Identification Phase
May 5 | Results Announced

Why you should participate

Every observation and identification can contribute to biodiversity research. Data on iNaturalist is available to anyone and is also shared with scientific data repositories such as the Global Biodiversity Information Facility. Data is also often used on a local scale and can help inform management decisions that help protect our environment. By participating, you are not only contributing to urban biodiversity science but also learning about your local environment!

Several organizations in the Denver-Boulder metro region have come together this year to host events related to the CNC! But you don’t have to attend an event to participate; observations can be made at your local park, in your backyard, or along your streets’ greenway! Or if you’re interested in identifying species, you can do that in the comfort of your own home after the observations have been made by others in our city.

Our Goal for 2025

Within the Denver-Boulder metro region, we hope to make 6,000 observations of animal, plant, and fungi life. We aim to have 600 observers take part in the observation phase, and 600 identifiers in the identification phase. By the end of the event, we hope to have 75% of all observations be considered research grade. Help us make our goal a reality by joining an event or participating on your own!

Join an Event

Colorado Open Lands
Urban Living Landscapes with South Suburban Parks and Recreation
Friday, April 25 | 11am – 1pm
South Platte Park, Littleton
Learn more!

City of Longmont Open Space
City Nature Challenge Ongoing Event
Friday, April 25 – Monday, April 28
Learn more!

Denver Audubon
City Nature Challenge Bioblitz in partnership with High Line Canal Conservancy
Saturday, April 26 | 9 – 11am
Bob Taylor Eco Area, Littleton
Learn more!

Denver Parks and Recreation
City Nature Challenge Bioblitz in partnership with High Line Canal Conservancy
Saturday, April 26 | 11am – 1pm
Bible Park, Denver
Learn more!

CSU Extension – Jefferson County
City Nature Challenge Bioblitz
Sunday, April 27 | 12 – 3pm
South Table Mountain
Learn more!

City Nature Challenge ID Party
Thursday, May 1 | 5 – 7pm
Jefferson County Fairgrounds CSU Extension Office, Golden
Learn more!

High Line Canal Conservancy
City Nature Challenge Bioblitz in partnership with Denver Audubon
Saturday, April 26 | 9 – 11am
Bob Taylor Eco Area, Littleton
Learn more!

City Nature Challenge Bioblitz in partnership with Denver Parks and Recreation
Saturday, April 26 | 11am – 1pm
Bible Park, Denver
Learn more!

Participate on your own

All you need is a smartphone and the iNaturalist app. Any observations (can be a photo or sound recording) you take between April 25 and 28 will count towards the project. You have up until May 4 to upload your observations and identify as many observations as you can. Any observations made within the seven-county Denver-Boulder region boundaries (Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas and Jefferson) on the dates above will automatically be added to our city’s project.

Don’t live in the Denver-Boulder region? You can still participate by joining other “cities” such as the CO Western Slope Project, Fort Collins Project, or Global Project.