Officers were called at 3.06pm to Old Dee Bridge, Handbridge, following reports of an assault.
A 14-year-old boy sustained serious injuries and has been taken to the Countess of Chester Hospital. A 15-year-old has been arrested on suspicion of section 18 assault and is currently in police custody.
Officers remain in the area whilst enquiries are ongoing and Old Dee Bridge is currently closed. Anyone with any information is asked to call Cheshire Police on 101, quoting incident number IML 433282.