A fresh outbreak of toxic green algae at a country park has raised new questions about the use of the location at next year's Commonwealth Games.

Strathclyde Loch is to host hundreds of athletes competing at the triathlon when the Games are staged in Glasgow between July 23 and August 3 next year.

Games organisers and North Lanarkshire Council insist plans are progressing to make the venue safe for competitors. But locals and visitors have continued to raise concerns about the state of the loch which has turned blue-green due to toxic algae, raising fears the water is unsafe for swimmers.

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This weekend's Great Scottish Swim, taking place at Loch Lomond, has previously been held at Strathclyde Country Park, but has moved because of levels of algae there.

One person who contacted The Herald last week complained of the state of the water. Former firefighter John Dyer said: "I have swum in open water for years and I have never seen it so bad. I'm really glad the Great Scottish Swim is now at Loch Lomond."

Plans to place a temporary dam in Strathclyde Loch to deal with the problem have been replaced with a barrier option, costing one-third as much.

North Lanarkshire Council says it will not stop the amount of toxic blue-green algae, which makes the water unsafe for swimmers, but would make it "easier to treat" if it becomes a problem.

The organisers of Glasgow 2014 were sufficiently worried about the loch to start considering other sites in March, last year.

Glasgow 2014 yesterday refused to discuss the existence of a Plan B and whether there was a deadline set for Strathclyde Loch to be ready and safe for the triathlon.

But North Lanarkshire Council shrugged off the algae threat. A spokesman said initially it was unaware of any major problem this year, and later said: "They tell me they have not seen any green this year. They say [the loch] is a slate blue colour. We are not alone in that. Everyone with open water has problems with algal bloom. It is not unique to Strathclyde Loch.

"We expect the blue-green algae, which has not been as prolific this year despite the hot spell in early July, to disappear within the next couple of weeks, helped by cooler weather."

Some £1.2 million has been set aside to tackle the algae, which can cause skin blister, vomiting and abdominal pains. Some 57 swimmers fell ill there in June, last year. Officials still believe it is a "fantastic venue" for the triathlon, which features a 1500m (1640yd) swim, 40km (24-mile) bike ride and 10km run.

It has been confirmed work has begun on creating a £370,000 barrier next to the finishing tower near the Water Sports Centre made up of pontoons, anchors and a low permeable membrane.

North Lanarkshire Council says the barrier will be in place by the end of October and it was ready to treat algae if it is a problems in summer next year, using "treatments available" including a potential further £900,000 requirement for UV treatment.

A council spokesman said: "We could end up with no bloom at all. All we can do is put in the best that we can. We may well get algal bloom as we may get it in other parts of the loch or other open waters across North Lanarkshire. But the plan is to create an a smaller, more easily, treatable area, if any bloom does appear."

Jane Moncrieff, chief operations officer of Triathlon Scotland said: "It has to be, it will be ready. We have an event on July 23 and Glasgow 2014 have assured us the solution which they have now reached will be in place and that water quality will be fit for the triathlon come those days."

A spokeswoman for Glasgow 2014 said: "We are confident the solution identified will ensure the loch meets the international standards required for elite athletes and deliver a fantastic Commonwealth Games competition venue.

"The solution has the backing of the Scottish Environmental Protection Agency and the Scottish Government. As part of the process we are developing contingency plans to mitigate against risks and issues."