The park is named for Dagny Johnson, a local environmental activist, approximately a year before her death in 2003. Through the 1970s, 80s, and 90s, Dagny led the Upper Keys Citizens Association and several other organizations that fought to stop the development that was planned for much of north Key Largo. Preservation of onshore communities was not the only purpose for protecting north Key Largo. The reefs offshore of developed areas in the Keys have been declining rapidly, and those off undeveloped north Key Largo remain in far better condition than most.