Police said the incident happened just before 3.30pm.
A police spokesperson said: “A jet ski and a RIB (rigid inflatable boat) were reported to have collided near Brighton Pier, and the woman on the jet ski was reported to have been injured.
“Emergency services attended the scene and the woman was taken to hospital with injuries, which were not assessed as life threatening.
“The occupants of both vessels are understood to be known to each other and the collision is currently being treated as accidental.”
The RNLI announced on Tuesday, August 2, that a volunteer crew from Brighton RNLI attended the incident, which happened south of Brighton Palace Pier.
An RNLI spokesperson said: “On arrival, the crew found an injured female casualty in the water and an assessment of the person was made.
“Also on scene was BHCC’s Lifeguard patrol boat, which was joined by HM Coastguard rescue helicopter from Lydd.
“The helicopter lowered their paramedic and specialist equipment to the lifeboat.”
The RNLI said the woman was brought onto the lifeboat and taken to Brighton Marina where South East Coast Ambulance Service took over.
Roger Cohen, lifeboat operations manager, said: “Firstly, the whole crew give their best wishes for the recovery of the casualty.
“I’d also like to add that I am proud of the team that attended the tasking who acted quickly and professionally, our frequent and thorough training kicked in to ensure we knew what to when faced with an injured person in the water.”
The B class Atlantic 85 relief lifeboat Ted Dawber, currently used by the crew at Brighton, returned to the station at 4.15pm, said the RNLI.
The RNLI has advised people who see anyone in trouble on the beach or sea to call 999 and ask for the Coastguard.
It has also urged people taking a craft to sea to always let people know where they are going and when they will be back, as well as taking a device for calling for help.