The app will allow residents and tourists to check water quality at 80 beaches and waterways. It will be available for smartphones, iPads and tablets.
Similar maps are already available for computers on the county government and San Diego Coastkeeper websites.
The sites use information from the county Department of Environmental Health, which tests coastal waters and posts warning signs when contamination is detected.
Beaches in San Diego County can be contaminated by runoff following rainstorms. In the southern part of the county, beaches are sometimes fouled by their proximity to the Tijuana River.