OVER 50 people took ill after taking part in an open water swimming event at Strathclyde Loch.
They suffered sickness, stomach cramps and diarrhoea following the race which attracted 70 entrants from across Scotland.
None of those affected are thought to have been hospitalised, however, the loch has now been closed to water sports and boating.
The next major event at the loch – to be used in 2014 to stage the Commonwealth Games triathlon – is the Great Scottish Swim on August 25.
Some of those who fell sick tested positive for norovirus, better known as the winter vomiting bug. Experts believe heavy rain prior to the event may have contaminated the water.
A Motherwell Masters Amateur Swimming Club source said six members of their club took part and were “very ill.” They had to seek medical advice following the event and some were off work for a week, she added.
The event, the Western Districts Open Water Swimming Championships, took place on June 23.
Adults and juniors took part in races of up to 4000 metres. Organisers had laid on a 1000-metre novices event, for those aged 12 years plus who had not tried the sport before. Juniors aged 13 to 16 years raced over 2000 metres.
A spokesman for NHS Lanarkshire said of the 70 people who took part in the event, 57 became unwell. They suffered gastroenteritis and reported symptoms of abdominal cramps, nausea, vomiting and diarrhoea.
Symptoms started on June 24 and June 25 and “tended to resolve after 24 to 36 hours”, explained the spokesman.
Norovirus – the UK’s most common stomach bug – has been identified from samples from five race participants.
A dozen of those taking part in the race were from Lanarkshire.
The spokesman added: “All participants from the event were contacted and given health advice and information about how to prevent further spread of infection. No-one who became ill is known to have required admission to hospital.”
The outbreak was discussed on June 26 at a meeting attended by representatives of NHS Lanarkshire, North Lanarkshire Council, the Scottish Environment Protection Agency, Scottish Water and Health Protection Scotland.
Experts believe illness among participants could be linked to heavy rainfall between June 21 and June 23.
Council officials say the loch’s water was tested on June 11 and June 21. Both tests showed the water was “well within acceptable open water swimming guidelines”.
A North Lanarkshire Council spokesman said all water sports, including boating as well as water ski-ing and windsurfing, have been suspended.
She continued : “We are working with NHS Lanarkshire and others to monitor water conditions and will publish on our website updates about activities on the loch, as they become available.”
The Great Scottish Swim is set for August 25. A spokesman for Scottish Swimming said all their open water events are subject to water quality checks.
He continued: “Strathclyde Park Loch is subject to a strict and regular water quality checking regime and we had access to enhanced levels of information for this event.
“None of the reports from the tests carried out before the event indicated that there was any reason to cancel it.
“Despite all the available reports prior to the event returning results well within our parameters, we still experienced a high level of illness.”
The spokesman added: “We are confident what we faced at Strathclyde was an extremely rare occurrence which hasn’t previously been experienced in Scottish Open Water swimming.”
It is not the first time there have been problems with open water swim events at the loch.
Blue green algae growth caused the cancellation of the Great Scottish Swim in August, 2010. Last summer algae growth put a stop to water sports activities at the loch.