TOXIC algae has contaminated the canal in East Lancashire prompting a major health warning.
People are being advised to avoid contact with the Leeds and Liverpool Canal.
The outbreak is the latest blow to hit the waters which remain closed due to 'water shortages'.
And the restrictions are being partly blamed for the extent of the blue green algae outbreak.
British Waterways said the lack of water movement had allowed the water to stagnate and bacteria to grow, while high winds helped it to spread.
An MP urged officials to do all they could to get the canal re-opened as soon as possible in a bid to tackle the problem.
However it appears that the 60-mile stretch from Wigan to Gargrave, through Chorley, Blackburn, Hyndburn, Burnley and Pendle, will remain closed until October at the earliest.
British Waterways said that people should not come into contact with the water. The bacteria can leave people seriously ill and anyone affected is being urged to see a doctor.
Direct contact may cause allergic reactions including itchy eyes, skin irritation and hay fever like symptoms as well as stomach upsets.
The algae can also be fatal to dogs and other animals.
Worst affected areas are waters at Rishton and Barrowford. Warning signings have been put up.
Andrew Stephenson, MP for Pendle, said: "It is a serious issue, so putting up a lot of signage is the best thing they can do at the moment.
"I hope the canal is reopened as soon as possible, but British Waterways has indicated that we could still be looking at mid-October before it happens.
"I think British Waterways are doing a good job of managing the situation and have every confidence in them."
Rishton councillor Stan Horne said: "It is down to British Waterways to combat it and people should give it a wide birth.
"But what about the ducks and wildlife that are on there?
"Children shouldn't play around there and people shouldn't go walking their dogs in case they drink or go in the water if it is dangerous."
Cath Ferguson, environment manager for British Waterways, said users must remain vigilant.
She said: “British Waterways is asking visitors to the Leeds and Liverpool Canal and its reservoirs to continue to enjoy the waterways, but avoid contact with the water.
"If members of the public do come into contact with blue-green algae affected water, they should remove all contaminated clothing and wash all exposed skin with clean water as soon as possible, and particularly before eating or drinking.
“If they are in any doubt about their welfare after contact with algae, they should seek medical advice. Farmers and pet owners should ensure that their animals do not have access to affected water.”
Blue-green algae occurs naturally in many inland freshwaters.
But Mrs Ferguson said there was now so much algae on the canal that it had resulted in a ‘bloom’ which colours the water green, blue-green or greenish brown.
This paint-like scum can be capable of producing toxins. It is not possible to tell from its appearance whether a bloom is harmful.
The canal locks were closed after a dry first seven months left reservoirs that feed the waters 10 per cent full.
Levels should be at 80 per cent.
Despite the hose pipe ban being lifted, restrictions remain on the canal because it will take longer for its reservoirs to be replenished.