Passengers on a pleasure cruiser had to put on life jackets when the boat started taking on water off Dorset.
Rescue boats were alerted to help the Dorset Belle which had six people on board as it approached the entrance to Poole Harbour on Wednesday evening.
The boat's skipper managed to start pumping out the water and the vessel was escorted back to shore safely.
It is believed the leak was caused by a faulty seal but an investigation is under way.
Watch manager Ros Evans said: "Although on this occasion the problem was only a relatively minor leak, the skipper acted correctly and calmly meaning that we were able to get assistance to him swiftly."