Twenty-six speeding vessels have been stopped by patrols in the Exe estuary since March.
Irresponsible boat and jetski owners are said to be speeding close to wildlife refuges and some have refused to stop when challenged by harbour patrols.
The scale of the speeding is outlined in a report to Exeter City Council by its harbourmaster Grahame Forshaw.
His report says that since the last meeting of the council’s harbour board in March a patrol boat has been on the water every weekend, weather permitting, and 26 vessels were stopped and their owners spoken to.
The number is slightly down on the same period last year.
Mr Forshaw’s report goes on: “The patrol boat can only be in one place at a time.
“We receive reports daily about vessels travelling at excessive speed. In fact when we are afloat working from our other boats, we see craft going too fast in the river, often in areas where there are moorings or close to the designated wildlife refuge areas.
“We have had occasions when skippers of vessels travelling too fast have refused to stop when requested to by the harbour patrol.”
The report also says that since March two broken-down vessels have been towed back to their moorings; one yacht sank on its mooring; a rowing boat and a powerboat collided and two yachts grounded on Pole Sands between Dawlish Warren and Exmouth.
A navigation buoy broke free from its anchor and drifted five miles out to sea before being recovered off Lyme Regis.
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