The PSNI was called to Donaghadee Harbour after a boat reportedly "knocked paddle boarders into the water" on Saturday.
Bystanders said that a speed boat came out of the Harbour 'at speed' on July 25 causing a 'disturbance' to swimmers in the area.
Local councillor for the area, Mark Brooks said someone could have been 'seriously hurt' following the incident.
The UUP councillor told Belfast Live: "There were local swimmers in the water at the time, including the Chunky Dunkers and a North Channel Swimmer, who was in the midst of training.
"It was reported to me that paddle boarders were affected.
"It was quite dangerous and it frightened people at the harbour. Everybody has the right to use the water.
"I would urge everyone to be careful and think of others when using it."
It is understood that members of the PSNI and Coastguard were on the scene on Saturday evening trying to speak with an individual relating to the incident.
A PSNI spokesperson said: "The Coastguard made Police aware of a report they had received in relation to the manner in which a boat was being operated in the water at Donaghadee Harbour.
"There are no further details at this stage."
