Hampshire gendarmerie along with coast guard, lifeboat and paramedic teams rushed to the scene after the distress call.
Twelve people were injured in the accident and were taken ashore for treatment.
The teenager was taken to hospital but later died of her injuries. His next of kin have been informed and are supported by specialist officers.
An investigation into the incident is now open.
A police statement said: “We are working with the Coast Guard and Marine Accident Investigation Branch following a RIB-to-buoy collision at Marchwood Marina, Netley at around 10 am 10 this morning (August 22).
“Twelve people who were on board were then taken to hospital.
“Unfortunately, one of the passengers, a 15-year-old girl, was pronounced dead in hospital.
“The girl’s next of kin have been informed and are being supported by specialist officers from the Hampshire Constabulary.
“Investigations into the circumstances are still ongoing and we would ask anyone who witnessed the incident, or possibly captured footage of it, to contact police immediately on 101, citing incident 554 of the date. today. ”
A spokeswoman for HM Coastguard said: “Three lifeboats, a Coast Guard rescue team and the ambulance service have all been called in to help.
“There were some injuries and the 12 people on board were taken ashore and handed over to the ambulance service. The Directorate of Marine Accident Investigation has been informed. “