Scott Keen from Morden was also found guilty of obstructing a boat race and interfering with the safety of persons gathered.
He also failed to comply with a harbour master’s notice or register his boat, the Barney McGrew, for use on the Thames.
The court heard how Keen was advised by an umpire that the river was closed and he should return to a navigation channel.
He ignored the request, cut across the racing line and narrowly missed one of the boats, which had to take last-minute evasive action.
His cruiser then caught the anchor rope of a race stake boat, before he stopped and launched a foul-mouthed tirade against participants.
Environment Agency officers invited Keen to a voluntary interview but he failed to attend.
Maria Herlihy, operations manager at the Environment Agency and harbour master of the Thames, said:
“This incident was a disgrace. Keen showed no regard for the safety of other river users and could easily have caused a tragedy. Quite frankly, it was no surprise to discover that his boat was unregistered, and we are happy with the court result.
“We hope that this serves as a clear warning to all – anti-social and dangerous behaviour on our rivers will not be tolerated, and we will take robust action to deal with those who disregard the rules and regulations for boating on the River Thames.”
The magistrates fined Keen the maximum penalty of £1,000 for interfering with the boat race and navigating his boat without due care and attention. The court explained that it used its discretion to go outside the sentencing guidelines to deal with the matter robustly.
The court heard the incident was shocking in its totality, with clear criminality that endangered the safety of other people, including the young people involved in the regatta.
The court also complimented the Environment Agency’s investigation, and the evidence submitted.
Also charged in court, on the same day, for separate and unrelated incidents was Paul Campbell of West Molesey, who was found guilty in his absence of having not registered his boat, Enigma, for 2024 and failing to comply with directions to move his vessel from its location at West Molesey riverbank. He received a total of £2024.24 in fines, compensation and costs to be paid within 28 days.
Ms Herlihy added:
“As these prosecutions show, we have no hesitation in bringing offenders to court who avoid their obligations and responsibilities to lawful river users. Just one day in court has resulted in more than £6,000 of fines and compensation, which should serve as a major deterrent.”
