Police are issuing a warning after reports of youths jumping into the water at Warkworth Harbour.
Officers have been called to the area, in Amble, after being alerted by the Harbour Master, boat drivers and members of the public.
Acting Inspector Sharon Wilmore-Greaves said that police have issued a number of dispersal orders to try to tackle the issue.
She added that those who jump into the harbour are putting their lives at risk.
She said: “We have had reports of children jumping in the harbour at Amble.
“They are at risk of getting injured by boats coming into the harbour by the propeller or run over. We want to raise awareness about the dangers of not knowing what’s underneath the water, different currents and riptides, boats using the narrowing waterway and coming into very close contact with youths swimming because they can hardly be seen.
“You may swim well in a warm indoor pool, but that doesn’t mean you can swim in cold water.
“Cold water can kill you in less than a minute and it can be difficult to estimate the depth of the water.
“There may be hidden rubbish under the surface that can trap or cut and it can be difficult to climb out as banks can be steep, slimy and crumble away.
“Also, the water may be polluted, which could make you ill, and there are no lifeguards.”