The deaths of four people on a paddleboarding trip was "tragic and avoidable", a report has said.
The organisation of the trip on the River Cleddau on 30 October 2021 was strongly criticised by the Marine Accident Investigation Branch MAIB.
Paul O'Dwyer, 42, Morgan Rogers, 24, Nicola Wheatley, 40, and Andrea Powell, 41, all died as a result of the trip in Haverfordwest, Pembrokeshire.
An inquest into their deaths was adjourned to allow investigations.
Mr O'Dwyer, from Port Talbot, Ms Rogers, from Merthyr Tydfil, and Ms Wheatley, of Pontarddulais, all died at the scene in Pembrokeshire.
Ms Powell, from Bridgend, died in hospital on 5 November 2021.
MAIB chief inspector Andy Moll has now said the accident was "tragic and avoidable".
Mr O'Dwyer, an Army veteran, was one of the leaders of the excursion, organised by the Salty Dog Company of Port Talbot, and was travelling at the rear of the group.
The other leader survived the tragedy.
Nine paddleboarders set off at about 09:00 - there were two leaders, the wife of one of the leaders and six paying participants.
Four paddleboarders got into difficulties at a weir on the western Cleddau, outside County Hall.
They were trapped by "hydraulic towback, with no means of escape," the report stated.
Although the leaders of the group were experienced paddleboarders, they had "no experience to teach novices on fast-flowing rivers".
The MAIB said the leaders' planning and preparation was inadequate and overlooked the extreme hazard posed by the weir.
They did not have adequate training, experience or qualifications to lead the group from Haverfordwest to Burton Ferry.
Signs at the launch site and on the river were said to be inadequate, along with clothing and buoyancy aids.
The MAIB also criticised UK stand-up paddleboarding, saying safety messaging and training governance was inconsistent.
Several safety recommendations have been made by the authors of the report, including risk assessments from Welsh Water in collaboration with Pembrokeshire council and Milford Haven Port Authority.
Ch Insp Moll said stand-up paddleboarding was one of the "fastest-growing UK watersports", with a 300% increase in numbers in recent years and urged participants to be aware of the risks.
"Firstly, wear the right equipment. Always wear a buoyancy aid," he said.
"In certain conditions, weirs can develop treacherous hydraulic towbacks that can trap and drown you."
After the deaths, a woman was arrested on suspicion of gross negligence manslaughter and released. Prosecutors are still considering whether charges will be brought against her.
Pembrokeshire council said it had taken further steps, ahead of receipt of the MAIB final report, by putting up more warning signs on the banks of the river upstream from the weir.
"Along with other organisations, the council has made itself available to assist Dwr Cymru Welsh Water, which owns and is responsible for the weir, in preparation of the risk assessment which was the recommendation from the MAIB.
"The matter remains in the hands of HM Senior Coroner for Pembrokeshire and an inquest will be held in due course. It would be inappropriate to comment further pending that process."
Following a separate and unrelated inquest into another paddleboard death on Wednesday, coroner John Gittens said he noted similarities between the two cases.
Following the death of 24-year-old Emma Powell in July, Mr Gittens said he would write to Tesco, where Ms Powell bought her board, and the UK government regarding his concerns over safety.