Police are looking for a man who dangerously rode a personal water craft near a beach and moored yachts, speeding past children in a canoe.
He was believed to have been speeding at 30 knots in a stretch of the river Blackwater near Steeple, where the limit is eight knots.
At one point, the craft passed between a man who was standing waist-deep in the water and children in a canoe only a few yards away.
It also passed close to the beach, a pontoon off Marconi Sailing Club and rows of moored yachts.
The incidents were on Saturday, June 7 at 6.41pm when the craft was being driven downstream towards Bradwell and at 6.59pm where it was driven back upstream.
Call the Essex Police Marine Unit on 101, or 999 in an emergency.