"Sooner or later someone will be killed," he said.
Mr Hollis regularly fishes on the Taieri, near Henley, using his 3m-long aluminium dinghy, in order to relax and get fresh air into his lungs, which have been damaged by a neurotoxic condition arising from previous work-related solvent exposure.
The Queenstown Lakes District Council plans to introduce a bylaw to make lifejacket use compulsory on boats by the end of summer.
The council announced that move after a fatal high speed collision between a private jet-boat and jet ski on a bend of the Kawarau River, near Frankton, on the evening of January 5, which killed two men aboard the jet-boat.
Two Invercargill jet ski riders were injured and are receiving treatment in Dunedin Hospital.
The collision is under investigation.
Mr Hollis contacted the Otago Daily Times and said that, given the recent fatalities, he was particularly concerned about two recent incidents on the Taieri River.
He saw three riders of jet skis, travelling close together at high speed, round a blind bend on the incorrect side of the river, immediately upriver of the John Bull Gully picnic area.
He said they could have hit him head-on, but because he had had previous experience of "cowboys coming round that particular bend", he had avoided them by travelling in the middle of the river, rather than on the regulation right-hand side.
The jet skiers also ignored the regulation which required river users to reduce their speed to five knots if passing within 50m of another craft, he said.
"To take a blind bend at full speed is sheer stupidity."
Mr Hollis had also seen a man riding a jet ski at high speed and towing on a long line two young people on a "biscuit".
The man did not have the observer aboard who was required to monitor the tow at all times.
At one point one of the young people fell off into the river, and this was not noticed straight away, he said.
More safety education was needed, he said, and a sign offering safety information should be installed at the main boat launching ramp used by the public in the Henley area.
Another nearby ramp, which was used by the Milton Boating Club, did have a sign giving some boat speed information.
He also agreed with a recent suggestion by Queenstown Lakes District Council harbourmaster Marty Black that safety lessons should be mandatory before powered craft capable of exceeding five knots could be operated on New Zealand waterways.
Otago Regional Council corporate services director Wayne Scott appreciated the safety issues raised by Mr Hollis and said the council would consider adding an information sign near the boat ramp.
Water safety education and taking personal responsibility were key points and there was already "a fair bit of awareness" about safety issues among boat users and jet ski riders.
Nevertheless, he was concerned that some people were wilfully breaking safety rules.
Early this year there would be public consultation on a review of the council's navigation safety bylaws.
An updated system could include instant fines, he said.
Mr Hollis said many river users were well behaved and considerate.
But in the five years he had been boating on the Taieri he had noticed a big rise in the overall number of boats and jet skis, and an equally big increase in the "arrogance" and aggression of some river users.
"They are just asking for trouble and sooner or later it's going to happen," Mr Hollis said.
