A number of dead geese were found along the Ashton canal this week - prompting concern from local residents.
The RSPCA recovered two dead and three sick geese, which later had to be put down, from the canal on Monday afternoon.
On Tuesday another three birds were found dead, and today, a further two.
Many people took to social media to say they had come across dead birds and fish, or seen them acting very strangely.
Animal Collection Officer, Jessica Pierce, says a deadly disease called Avian Botulism is responsible.
Speaking to the M.E.N, she said: "Because of lockdown there aren't as many boats going through which means the water in the canal has less oxygen.
"When you combine that with the intense hot weather we've had, the bread and food that is getting thrown in goes rotten.
"The geese eat the food and it causes something called Avian Botulism."
Jessica says the disease would explain why many people have seen the birds acting strangely, or looking 'dazed.'
"It paralyses their legs and then their neck muscles and they become very unwell," Jessica explained.
"It is hard to say stop feeding the geese but I would advise not feeding them at the moment.
"People feed them all sorts - I have seen people feed them curry and rice. I would advise sticking to corn but they do have plenty of canal wildlife to feed on too.
"I am hoping now we have had the rain there won't be a massive problem."
Jessica says she and her colleagues will be going out to the canal daily to check on the geese, as the paralysis can come on very quickly.
"If we can catch them early enough then sometimes we can treat it before it becomes fatal," she said.
Jessica saw the same thing last year at Boggart Clough in Blackley and at Alexandra Park the year before, where around 100 geese died.
She is urging anyone who sees the birds acting strangely to phone the RSPCA immediately.
